Indicator palettes from Omarchy themes

The problem

Omarchy is a Linux desktop that is themed as a whole: pick Nord or Gruvbox or Catppuccin and the terminal, the editor, the window borders and the bar all change together. Each theme is a small file of named colours, mostly the sixteen a terminal expects: red, green, yellow, blue, magenta, cyan and their bright variants, plus a background, a foreground and an accent.

omacharts draws market charts, and it follows that theme. The chart's background, grid, text and candles all come from the file, so the app looks like it belongs on the desktop it is running on. The hard part is the indicator palette: when you add a moving average, then another, then a band and an oscillator, each one needs a colour, and those colours have to do several things at once. Each must be visible as a line one or two pixels wide against the chart. Each must be distinguishable from every other, because overlays cross and run beside each other. None may look like the candles, whose green and red already mean up and down. And the six together should look like they were chosen by whoever designed the theme, not dropped on it from a box of crayons.

Six distinguishable colours on one background is harder than it sounds. A terminal palette was never designed for it: its colours are meant to be read as text, a few at a time, and plenty of themes do not even try to offer six hues. Lumon is six shades of one blue. Lupine's "yellow" is blue. Hackerman's "red" is green. Vantablack has no hue at all. And in thirteen of the 22 themes, cyan and bright_cyan are the same hex.

Before and after

The original derivation extracted: the Blue slot took the theme's blue, Amber took yellow, and so on, then nudged anything that collided. The rewrite generates. The theme still decides almost everything: how light the lines are (where its own colours sit, pulled into the range that can be seen on its background), how vivid they are (as vivid as its own colours, within a band), and, whenever it has a colour near enough to what a name means, the hue itself: Nord's Blue is Nord's blue. Only when the theme has nothing to offer for a name is a hue invented, and then it is the hue the name promises, at the theme's own lightness and chroma. All of it happens in OKLCh, a colour space built so that equal steps look equal, which is what makes "same lightness, different hue" mean what it says.

How to read the measurements

Two numbers appear throughout. ΔE is the distance between two colours in OKLab, on a scale where black to white is 1.0. About 0.02 is the smallest difference an eye can see; two thin lines closer than about 0.06 read as the same line in two places; the generator guarantees every pair of automatic overlays at least 0.08, and at least that from each candle colour, and 0.06 from the grid, the axis and the crosshair. Contrast is the WCAG ratio against the chart background, where 3:1 is the accepted floor for graphics that carry meaning; every line is held to at least 3:1. L, C, H are a colour's OKLCh lightness (0 to 1), chroma (0 is grey; 0.09 is a quiet colour, 0.2 a vivid one) and hue in degrees.

In each theme below, the left panel is the old derivation and the right is the current one, drawn on the theme's real chart background with its grid, axis, crosshair and candles. Numbers below a guarantee are marked like this. The old derivation is shown in full, including the themes where it was already fine; the summary table is the honest version of the argument.