# colour on a drawing, what we learned

how engineers actually use colour on drawings, from the sources below and from roebling's own 1870 sheets in `brooklyn-bridge/source`. read before touching the palette.

## 1. the issued sheet has no colour

an issued drawing is black on white. it is plotted monochrome; colour does not survive the plotter, the copier, the blueline. meaning on the sheet is carried by line: weight, dash, halftone.

| on the sheet | drawn as |
|---|---|
| new work | full weight |
| existing to remain | halftone, grey |
| demolished | dashed |
| a revision | cloud and delta, still black |
| the seal | ink or embossed |

colour is never the drawing. colour is the conversation about the drawing.

## 2. the check print: colour is what kind of speech

the drafting-room code, 20th century, still taught (genium drafting manual, whitmire 2005; fire tech; engineers edge; qbs). the checker marks a print with coloured pencils; the drafter picks up; the checker backchecks and signs the title block as "checker".

| colour | means | who |
|---|---|---|
| yellow | correct. read and it holds. laid over what was verified | checker |
| red | change this. add it, fix it, it must change. the origin of "redline" | checker |
| blue | comment. for information only, not to be drafted | checker |
| green | delete (one family of shops) · picked up (another) | varies |
| pencil / black | initials, dates, the drafter crossing off each pickup | drafter |

what is stable across every source: yellow is verified, red is the instruction to change, blue is the note that is not to be drawn. green is the unstable one. no universal standard exists; each shop fixes its own, and colour is only a guide, the notation must carry the meaning on its own (colour-blind readers, copies).

why these colours: reproduction. blue pencil did not copy (non-photo blue, the blueline era), so blue was safe for notes. red copied dark and was found first. yellow is transparent on a copy, so a highlight never hid a line.

## 3. roebling's sheets, 1870: three inks

the brand's hero drawings, `nypl-1870-*.jpg`. looked at, not read about.

| ink | on the sheet |
|---|---|
| black | the object. every line of masonry, timber, iron, the lettering, the wash |
| red | every dimension. the numbers, the dimension strings, the extension lines, the centre lines. what it must measure |
| blue | iron and steel, and water. the air shafts through the caisson, the water line |

this is the 19th-century material code (dean of guild drawings, british and american, 1800–1950): red brickwork, dark blue iron and steel, yellow wrought timber, brown masonry. it comes from vauban colouring the cut on a section. on roebling's sheets red has already moved from brick to the measure: red is what it should be.

## 4. now: bluebeam

no industry standard. agencies set colour per reviewer or per status, and configure it. odot: every staff comment blue, for uniformity; accepted turns green. port of portland: one colour per discipline, a status colour per state. red is still the default markup in every tool. the term of art is still "redline". the seal is signed in blue ink so the original can be told from the copy.

so "colour is who is speaking" is not a brand idea. it is how the industry already configures its review tools.

## 5. what it means for us

- ink is the drawing. the engineer's, and only ever black. the machine's lines turn to ink only when the engineer signs (the storyboard says it: the machine draws, the engineer signs. it is the check-print rule: blue is not drafted until the drafter draws it).
- red is the instruction to change. what should be. only the engineer writes it: the machine asks "is this what you meant?" in blue, and the red is the reply — the cloud, the size struck and rewritten, the number that does not hold. never decoration.
- blue is the note for information. what the machine read, what it answers, its reasoning, the lines it proposes. not drafted until the engineer takes it. also iron on roebling's sheet, and the original signature. every line of history lands blue on the machine's voice. and blue is the thread: the one quick stroke that ties a thing to what it means — a detail mark to its detail, an answer to its member, a line to the joint it names (`draft.thread`, `Sheet.thread`). the engineer's leader is ruled ink; the machine's is the thread.
- yellow is verified. the checker's highlight: read, and it holds. a wash behind ink, never a line. the one voice a trust product needs most.
- grey is existing. halftone is what is there and not in question.

three pens and a highlighter. the same kit every checker has in the drawer.

## 6. what else has colour in structural work

everything above is the check print. the rest of the trade has colour too, and each one is its own language.

| where | colour | means |
|---|---|---|
| the cad screen | aci 1–9: red, yellow, green, cyan, blue, magenta, white, greys | line weight. every colour is a pen; none of it means anything but thickness. it dies at the plotter |
| the analysis model | blue to red ramp | stress, deflection, moment: low to high |
| the design check (etabs, sap, ram, risa) | green · yellow · orange · red | demand over capacity. red is over 1.0: it does not hold |
| the clash model (navisworks) | red · green | hits · clear |
| the check print, less stable | green · orange · pink | delete · picked up · backchecked. shop by shop |
| the material code, 1800–1950 | yellow · brown · pale orange | wrought timber · masonry · rough timber. alongside red brick, blue iron |
| the paper | canary yellow trace · green engineering paper · blue and sepia print stock · mylar | the sketch before ink · the calc · the copy · the original |
| the seal | blue ink | the original, not the copy |
| the site | apwa paint: red electric, yellow gas, orange comms, blue water, green sewer, pink survey, white proposed | what is under the ground |
| the steel | red-oxide primer · green epoxy rebar · grey fireproofing | the member before it is covered |

what matters for us: the design check already says red is over capacity, in every structural program an engineer opens. red = does not hold is not our invention; it is the industry's. and the sketch before ink is yellow trace, the calc is green paper: the thinking has colour, the signed sheet does not.

## 7. the system, as applied

`styles.css` carries the drawer. names are the pens, not roles, because the trade names them that way.

| var | hex | class | the pen, see §5 |
|---|---|---|---|
| `--fg` | #111111 | `.fg` `.stroke-fg` `.patch` | ink |
| `--muted` | #808080 | `.muted` `.stroke-muted` `.patch` | grey |
| `--blue` | #0000cd | `.blue` `.stroke-blue` `.patch` | the note |
| `--red` | #cd0000 | `.red` `.stroke-red` `.patch` | the redline |
| `--yellow` | #ffe600 | `.yellow` | the highlight. a wash: there is no `.stroke-yellow` on purpose |
| `--bg` | #ffffff | `.bg` | the sheet |

one name per colour, and it sets text and fill together. `.patch` puts that same colour on the ground — `.blue .patch` is a blue swatch — so a colour is named once and never again as a background.

a link on the site is blue: a note pointing elsewhere. a field in focus is blue. nothing else on the site is coloured.

## sources

- gary whitmire, "checking drawings", genium design tips 031, 2005. yellow correct, blue comment, red must change. http://files.engineering.com/files/ac0e18da-9c9a-41b0-8f35-6b702ed4e28a/DESIGN_TIPS_031_-_Checking_Drawings.pdf
- fire tech, "color codes for marking up drawings". red add, green delete, blue information, yellow correct, orange picked up. https://blog.firetech.com/article-3-color-codes-for-marking-up-drawings/
- qbs as-builts, "how to interpret engineering drawing markups". https://qbsasbuilts.com/engineering/
- engineers edge, "engineering drawing checking". https://www.engineersedge.com/wwwboard/posts/3690.html
- cadtutor, "back drafting color codes". thirty-year practice, colour-blind caveat. https://www.cadtutor.net/forum/topic/29873-back-drafting-color-codes/
- eng-tips, "color coding markups on engineering drawings" and "colour used for hand marked updates". https://www.eng-tips.com/threads/color-coding-markups-on-engineering-drawings.325592/ · https://www.eng-tips.com/threads/colour-used-for-hand-marked-updates-to-engineering-drawings.383904/
- odot, bluebeam review guide, 2022. staff comments blue; accepted green. https://tas.transportation.ohio.gov/CADD/Manuals/ODOT_Bluebeam_Review_Guide_FINAL.pdf
- port of portland, bluebeam design review standards, 2019. colour per discipline, status states. https://cdn.portofportland.com/pdfs/203%20-%20Bluebeam%20Design%20Review%20Standards.pdf
- nyc department of records, "brooklyn bridge architectural drawings: material matters", 2020. black image, red measurements, blue steel. https://www.archives.nyc/blog/2020/11/6/brooklyn-bridge-architectural-drawings-material-matters
- mark chalmers, "colour conventions in architectural drawing", urban realm, 2022. the material code, vauban. https://www.urbanrealm.com/opinion/2022/07/06/colour-conventions-in-architectural-drawing/
- wikipedia: whiteprint, blue pencil (editing), non-photo blue, blueprint, redline. https://en.wikipedia.org/wiki/Whiteprint · https://en.wikipedia.org/wiki/Blue_pencil_(editing) · https://en.wikipedia.org/wiki/Non-photo_blue
- archisoup, "red line drawings"; young architect, "architectural redlines 101". the redline workflow, crossing off pickups. https://www.archisoup.com/red-line-drawings · https://youngarchitect.com/architectural-redlines-emerging-professional-101/
- red knight repro, "color coding construction drawings". existing grey, demo red, new blue; trade colours. https://redknightrepro.com/color-coding-construction-drawings/
- revit forum, existing vs new conventions; bim pure, revit phases. halftone existing, dashed demo. https://www.revitforum.org/forum/revit-architecture-forum-rac/architecture-and-general-revit-questions/12452-what-are-graphic-conventions-these-days-for-indicating-existing-vs-new-walls-color