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Choose black or white text on accents by WCAG contrast - #16
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`on_color` chose black or white ink with a cutoff on `luminance`, which weights the channels but leaves them gamma-encoded. That reads mid tones as darker than they are, so they got white where black has twice the contrast: 2.7:1 against 7.7:1 on Everforest's red, which fills the destructive buttons, and 3.2:1 against 6.5:1 on a plain #8f8f8f. It now takes the WCAG relative luminance, with the channels linearised, and picks whichever ink has the higher contrast ratio. `luminance` stays as it is for telling a light palette from a dark one, the only other thing it does. Light accents such as Everforest's, Catppuccin's, Tokyo Night's and Nord's already got black and are unchanged. A saturated mid blue like GNOME's #3584e4 flips to black as well, 5.6:1 against 3.8:1. None of this touches a desktop without an Omarchy palette, where libadwaita's own colours stand.
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on_colorpicks black or white withluminance(c) > 0.6, on gamma-encoded sRGB values (weighted, but not linearized). For mid tones that often picks the worse ink.#8f8f8f, for example, gets white at 3.2:1 instead of black at 6.5:1. The red from the Everforest test palette (#e67e80) gets white at 2.7:1, which is what destructive buttons use.This picks whichever of black or white has the higher WCAG contrast ratio, using linearized relative luminance.
luminanceitself is unchanged, since mode detection still uses it.#8f8f8f#e67e80(Everforest red)#e06c75(One Dark red)#3584e4(GNOME blue)Light accents like Everforest, Catppuccin, Tokyo Night and Nord are unaffected; they were already black. Note that GNOME blue flips to black too, because white falls short of 4.5:1 there. This only affects Omarchy palettes; without one, libadwaita's own colors are untouched.
Before / after with a
#8f8f8faccent (checked toggle, today badge):Best landed after #14: with more reds getting black ink, destructive buttons need their fill back. The two merge cleanly in either order.
Test first (
on_color_picks_the_ink_with_more_contrast_on_a_mid_tone), then the four CI gates.