Klein blue is invisible as text — here's how I worked around it

I use Claude Code for hours every day, and most of what I read is prose — tool output, reasoning traces, permission prompts. Terminal themes are built for syntax highlighting: dark backgrounds with fine-tuned keyword colors. That's the wrong optimization when your screen is 80% English paragraphs.

I wanted a theme tuned for body-size prose legibility over long sessions, anchored to a single color I actually cared about: Yves Klein's IKB, the ultramarine pigment he mixed himself and patented in 1960. Pure IKB is hex 002FA7.

First thing I found: pure IKB fails as text on a dark background. APCA Lc score of -12 — effectively invisible. You can use it as decoration, borders, highlights. You cannot use it as readable text.

Claude Code maps its permission-prompt text to the terminal's ansi:blue slot. If I dropped IKB into ansi:blue, the prompts would disappear. So I split the role across two slots:

ansi:blue = 002FA7 // pure IKB — decorative borders, structural chrome