Spend a few hours in an AI coding assistant and count what's actually on screen. Tool output confirming a file write. A reasoning block working through a refactor. A permission prompt asking if you want to run bash. It's paragraphs — body-size prose, not syntax-highlighted code. Standard terminal themes are built for token colorization. That optimization is largely irrelevant when your screen is 80% English sentences.
I built klein-blue around that mismatch. Four .terminal profile variations for macOS Terminal.app, anchored on Yves Klein's IKB pigment, with contrast verified using APCA rather than WCAG ratios. APCA distinguishes between body text, subtle annotations, and decorative accents — WCAG doesn't, and the difference matters when you're reading prose for hours.
One concrete detail worth knowing: pure IKB (hex 002FA7) fails as readable text on dark ground — APCA Lc -12, effectively invisible. So I split it across two ANSI slots. The ansi:blue slot gets the pure IKB pigment for decorative borders and highlights where legibility isn't the point. The ansi:blueBright slot gets a lifted Klein-family A8BEF0 that clears the Lc 60 accent gate and lands on the permission-prompt text you actually need to read.
The four variations differ on one decision: what to do with ansi:redBright, which is the slot Claude Code uses for its claude-sand brand color. Klein Void Sand & Sea accepts it as a second hero color alongside IKB. Klein Void Refined neutralizes it so IKB is the only color competing for attention. Klein Void Prot is the strict version — every accent slot passes APCA gates, body text hits Lc 90+, subtle text Lc 75+. Klein Void Gallery pushes toward maximum void: one blue, everything else near-neutral.
Installation requires one non-obvious step: Claude Code's /theme picker must be set to dark-ansi. If it's left on the default, Claude Code ignores the Terminal.app ANSI profile entirely and uses its own hardcoded RGB palette.
git clone https://github.com/robertnowell/klein-void
cd klein-void
bash install.sh
# then in Claude Code: /theme -> dark-ansi
Rollback is bash restore.sh — it writes back whatever Terminal.app profile was active before install.
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