Klein-blue terminal theme optimizes for prose readability in Claude Code

J Now built "klein-blue" after observing that time spent in Claude Code is dominated by prose — tool output, reasoning traces, and permission prompts — rather than syntax-colored code. Standard terminal themes optimize for token-colored code where the eye jumps between short fragments, but prose reading demands higher contrast on body text, softer contrast on secondary text, and accent colors that don't fatigue the eye. The theme is anchored by Yves Klein's IKB pigment as a design reference.

The readable blue used for permission-prompt text is a lifted Klein-family color (`A8BEF0`) assigned to `ansi:blueBright`, which passes the contrast threshold.

The strictest variation, Klein Void Prot, requires every color role to pass APCA Lc gates: body text at Lc >= 90, subtle text at Lc >= 75, muted text at Lc >= 45, and accent at Lc >= 60. A key finding from the APCA analysis is that pure IKB (`002FA7`) is effectively invisible as text on a dark background — measuring Lc -12 — so IKB is confined to decorative roles (`ansi:blue`, borders, and highlights). The readable blue used for permission-prompt text is a lifted Klein-family color (`A8BEF0`) assigned to `ansi:blueBright`, which passes the contrast threshold. The four variations split on two axes: strictness of APCA compliance, and whether Claude Code's `claude-sand` brand color (which lands in `ansi:redBright`) is neutralized so IKB remains the sole hero color, or accepted as a second accent. The theme ships as macOS Terminal.app `.terminal` profile files paired with either CommitMono or IBM Plex Mono, and is available at the linked GitHub repository.

Key facts

1. 01Built by J Now to address the prose-heavy nature of Claude Code sessions, where syntax highlighting is largely irrelevant.
2. 02Anchored by Yves Klein's IKB pigment (hex `002FA7`), which the author wanted to look at all day.
3. 03Pure IKB scores Lc -12 on APCA — effectively invisible as text on dark backgrounds — so it is used only in decorative slots.
4. 04The readable blue for permission-prompt text is hex `A8BEF0` (`ansi:blueBright`), which passes APCA contrast thresholds.
5. 05Klein Void Prot is the strictest variation: body >= Lc 90, subtle >= 75, muted >= 45, accent >= 60.
6. 06The four variations split on whether Claude Code's `claude-sand` brand color (`ansi:redBright`) is neutralized or accepted as a second hero color.
7. 07Ships as macOS Terminal.app `.terminal` profile files with CommitMono or IBM Plex Mono; requires Claude Code's `/theme` picker set to `dark-ansi`.

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