Generating the cutout palette
The cutouts variant of the Training lesson leans hard on colour as a fast filter. Every word has its own colour, repeated wherever the word appears, so your eye can scan “what’s the colour of the word I just wrote?” before you read any text. It really helps with the needle-in-a-haystack aspect of the activity.
Until last month the palette held eight colours, hand-picked in OKLCH (TODO link) at a fixed lightness so white text would read on every coloured box. Green Eggs and Ham has about sixty unique tokens trying to share eight buckets, which works out to seven or eight words sharing each colour. Plenty of colour collisions, plenty of moments where you have to slow down and re-read.
I bumped it to 14 (still hand-tuned, two lightness levels) and that helped, but really this is a solved problem and I was reinventing it badly.
The new palette is algorithmically generated using Glasbey-style greedy max-min selection in OKLab. The algorithm samples 200k candidate colours uniformly from the sRGB gamut, converts them to OKLab (which is perceptually uniform by design, so plain Euclidean distance corresponds to perceived difference), then iteratively picks the candidate that’s furthest from every colour already chosen. Black and mid-grey are seeded as anchors so the algorithm can’t accidentally allocate “chromatic” colours that drift into greyscale.
The result is 30 swatches with a minimum pairwise OKLab ΔE of 0.137. That sits comfortably above the 0.10 “clearly distinct” floor, with headroom for the perceptual loss you get from CMYK conversion, paper colour, and ambient lighting. Print eats some of your distinguishability budget, and not always in proportion to OKLab distance.
A first pass let candidates roam from L=0.20 upwards and gave a slightly tighter min ΔE of 0.145. It also produced a dark blue at L≈0.275 that came out of the printer looking like black. CMYK reaches saturated deep blue by leaning hard on the K plate, so a small ink-balance shift collapses the colour onto pure black; the seeded black anchor protects against collisions in OKLab, not in CMYK. Raising the L floor to 0.32 trims four near-black candidates, costs about 0.008 of min ΔE, and leaves no chromatic entry close enough to merge with K in print.
Each palette entry is tagged as “light” or “dark” based on its OKLab L. The Typst renderer pairs light entries with black text on the coloured box and a thin black stroke on the free-standing word; dark entries get white text and no stroke. That adaptive treatment is what lets the palette extend up to L≈0.92, where the very light pastels live. Without it, every fill would have to be dark enough for white text to read on, capping the usable lightness range and so the achievable colour count.
The palette isn’t colour-vision-deficiency safe. CVD-safe palettes max out around 8-12 distinct colours, which would undo the whole exercise. If you’re working with a CVD-affected student, the grid version of the lesson uses no colour at all and reaches the same understanding.
The script lives in the repo at cli/scripts/generate_palette.ts: pure
TypeScript, Node 22.7+ native, no tsx or npm install required. The Typst
file that produces the cutouts has the resulting OKLCH triples pasted in
directly, with a comment pointing at the script for regeneration. Different N or
different lightness bounds, one line regenerates the palette.
The tools page has the four ready-to-print PDFs (Green Eggs and Ham and The Cat in the Hat, each in bigram and trigram), all freshly built with the new palette. If you’ve used the cutouts before, you’ll notice the difference straight away. If you haven’t, the previous post explains the activity.