Most of my Claude Code screen is English. Tool output, reasoning traces, permission prompts, explanations — paragraphs of prose I read for hours every day. Every terminal theme I tried was built to make syntax highlighting pop: high-saturation keywords, dim punctuation, short tokens scanned left-to-right. That's optimizing for the wrong thing when 80% of your screen is body-size prose.
So I built klein-blue — four Terminal.app themes tuned for Claude Code's specific ANSI slot layout, anchored to Yves Klein's IKB pigment.
The single most interesting problem was IKB itself. Pure IKB (002FA7) fails APCA contrast as text on a dark ground: Lc -12, effectively invisible. I wanted the pigment present without sacrificing legibility, so I split it across two ANSI slots — pure IKB in ansi:blue for decorative borders and highlights (no reading required), and a lifted Klein-family A8BEF0 in ansi:blueBright for permission-prompt text that actually needs to be read.
APCA governs every text role with per-role gates: body >= 90 Lc, subtle >= 75, muted >= 45, accent >= 60. The Prot variation (V3) is the only one where every accent clears strict gates. The other three make deliberate tradeoffs — the Sand & Sea variant accepts Claude's ansi:redBright brand color as a second hero rather than neutralizing it, which is the differentiating choice between variations.
git clone https://github.com/robertnowell/klein-void
cd klein-void
bash install.sh
# then set Claude Code /theme to dark-ansi
One required step that isn't obvious: Claude Code must have /theme set to dark-ansi. Without that, it ignores your Terminal.app ANSI palette entirely and falls back to a hardcoded RGB palette — your theme is invisible.
Ships as .terminal profile files, built from a variation-aware Objective-C builder (build.m), with restore.sh if you want to roll back. CommitMono-Regular on V1/V3, IBM Plex Mono on V2/V4, both installed to ~/Library/Fonts/.
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