After a few weeks of running Claude Code for most of my work, I noticed the thing that was actually tiring: not the code, the prose. Tool output, permission prompts, reasoning traces — it's paragraphs, not syntax. The terminal theme I was using was built for Python and Rust. It had no opinion about what comfortable body-size text looks like after three hours.
So I built klein-blue: four Terminal.app themes tuned for that specific reading experience, anchored to Yves Klein's IKB pigment.
The IKB problem turned out to be the interesting design constraint. Pure IKB — hex 002FA7 — scores Lc -12 on APCA against a dark ground: effectively invisible as text. You can't use it for anything readable. What you can do is split it: park pure IKB in the ansi:blue slot (decorative borders, highlights, places where legibility is secondary) and use a lifted Klein-family blue, A8BEF0, in ansi:blueBright (permission-prompt text, where you actually need to read it).
The four variations each answer a different version of the same question: what do you do with Claude's brand color — the claude-sand orange that lives in ansi:redBright?
Klein Void Refined neutralizes it. One blue hero, no competition.
Klein Void Sand & Sea accepts it as a second hero. IKB and claude-sand coexist.
Klein Void Prot is the strict one — every accent slot passes APCA gates (body >= 90 Lc, subtle >= 75, muted >= 45, accent >= 60). The version I use when I'm doing anything that requires reading carefully.
Klein Void Gallery goes the other direction: maximum void, one blue, no warmth anywhere.
Contrast is verified with APCA rather than WCAG because WCAG 2.x gets the math wrong at body size on dark backgrounds — it overestimates contrast for light-on-dark. APCA Lc gives numbers that track actual legibility.
Installation requires one non-obvious step: Claude Code needs /theme set to dark-ansi, otherwise it ignores the ANSI palette entirely and falls back to hardcoded RGB. The install script covers the fonts (CommitMono for V1/V3, IBM Plex Mono for V2/V4) and includes a restore script if you want to roll back.
MIT licensed.
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