Spend a few hours in Claude Code and the screen is mostly English — tool output, reasoning traces, permission prompts asking you to read and decide. Syntax highlighting is almost irrelevant. What matters is whether body-size prose stays comfortable after six hours of sessions.
Most terminal themes weren't built for that. They're tuned for token-colored code, where the eye jumps between short fragments. Prose reading is different: you need higher contrast on body text, tolerably soft contrast on secondary text that doesn't compete, and accent colors that don't burn.
I built klein-blue around Yves Klein's IKB pigment as the anchor color — a specific blue I wanted to look at all day. There are four variations, each making a different tradeoff. Klein Void Prot is the strict one: every color role passes APCA Lc gates (body >= 90, subtle >= 75, muted >= 45, accent >= 60). The others trade some strictness for aesthetics.
One thing APCA exposed immediately: pure IKB (hex 002FA7) is effectively invisible as text on a dark ground — Lc -12. So IKB lives only in the decorative slot (ansi:blue, borders and highlights). The readable blue — permission-prompt text and similar — is a lifted Klein-family color (hex A8BEF0) in ansi:blueBright, which actually passes.
The other differentiating choice is what to do with Claude Code's claude-sand brand color, which lands in ansi:redBright. Two of the four variations neutralize it so nothing competes with IKB. Two accept it as a second hero. That's the meaningful split between variations in daily use.
Ships as macOS Terminal.app .terminal profile files with CommitMono or IBM Plex Mono depending on variation. One prerequisite worth knowing: Claude Code's /theme picker has to be set to dark-ansi, otherwise Claude Code uses its hardcoded RGB palette and ignores your ANSI theme entirely.