The dark palette is hand-authored for C# only; every other highlighting
definition -- XML, IL, Asm, and all AvaloniaEdit built-ins -- is derived by
inverting HSL lightness. HSL lightness is not perceptual luminance, so the
result depended entirely on hue: blue carries a 0.0722 luminance weight, so
plain Blue landed at 4.08:1 against the editor canvas, and an already-light
source such as Asm's #8080FF inverted downwards to 1.29:1 -- invisible.
Reported against XML resources in #3986.
Enforcing a 5.5:1 WCAG floor on the converted foreground fixes every affected
definition in the one place they all route through, which a per-language
palette would not: the AvaloniaEdit built-ins (JSON, Markdown, JS, HTML, CSS,
Python) have no palette to author. 5.5 is where the existing CSharpDark values
already sit; the 4.5 AA threshold was measured and only moves the reported blue
to 4.51. The floor is deliberately foreground-only -- forcing a span background
to contrast with the canvas would repaint Asm's #EEEEEE Registers background as
a bright block and bury the text on top of it -- and it is measured against the
surface the foreground lands on, which is that span background when the colour
declares one, so a light-on-dark span cannot be pulled apart into two colours
that no longer contrast with each other.
The same function's desaturation guard only fired when the inverted lightness
stayed below 0.75, so a dark fully saturated source (DarkMagenta) came back
light and still fully saturated -- exactly the neon the softening exists to
prevent. Only the softening becomes unconditional; the lightness lift paired
with it stays scoped to over-saturated colours, because it is not monotone
across its own 0.75 boundary and would reorder neighbouring greys.
Hyperlinks were a second, unrelated path: nothing ever set
TextView.LinkTextForegroundBrush, so the About page and every decompiler-view
link used AvaloniaEdit's registered default of pure blue, 1.94:1 on dark. They
now share a themed ILSpy.LinkForeground with the metadata table's token cells,
which take it from a style rather than a local Foreground so the selected row's
white override still wins over the accent fill.
Assisted-by: Claude:claude-opus-5[1m]:Claude Code
Christoph Wille