A TUI RGB color picker. Two slots (foreground + background), R/G/B and H/S/V sliders, hex input, live sample-text preview, WCAG contrast indicator. Pure ANSI 24-bit truecolor — no kitty graphics dependency, works in any modern terminal.

Member of the Fe₂O₃ Rust terminal suite (landing page).

Features

• Two color slots. Edit foreground and background side-by-side, Tab to swap which one is active.
• RGB and HSV at the same time. Six sliders share one underlying color: nudge the hue and the R/G/B values move with it; nudge red and the hue/saturation/value follow. Pick whichever axis fits the job.
• Hex input. Press #, type six hex digits, Enter.
• Live sample text. A multi-line sample area renders the current FG-on-BG against realistic content (heading, code, comments, body prose, special characters), so you immediately see whether the pair is readable.
• WCAG contrast. The contrast ratio between FG and BG is shown with a level marker (AAA ≥ 7 / AA ≥ 4.5 / AA· ≥ 3 / ✗ low), so theme work doesn't ship unreadable pairs.
• Pipe-friendly output. On quit, the chosen colors are printed to stdout in your chosen format (hex / rgb / hsv / all). Use it to drive sed against a config file, or capture a single hex with prism --pick.
• Tiny. ~500 KB stripped binary. ~5 MB resident. No async runtime, no allocator hot path, no work between keystrokes.

Install

PATH="/usr/bin:$PATH" cargo build --release
ln -sf "$(pwd)/target/release/prism" ~/bin/prism

Usage

prism                    # interactive (pair mode, prints both slots)
prism --pick             # pick a single color (the FG slot)
prism --pair             # explicit pair mode (the default)
prism --hex              # output as #rrggbb (default)
prism --rgb              # output as rgb(R, G, B)
prism --hsv              # output as hsv(H°, S%, V%)
prism --all              # output all three formats
prism --out=FILE         # write the result to FILE instead of stdout
prism #f74c00            # preload FG with this hex
prism #f74c00 #0a0a14    # preload both FG and BG

On quit, the chosen colors print to stdout one per line, prefixed with the slot name (or to --out=FILE — see below):

$ prism --pick
color=#f74c00
$ prism --pair --rgb
fg=rgb(247, 76, 0)
bg=rgb(10, 10, 20)

This makes prism easy to script against:

# Update glassrc fg color
hex=$(prism --pick #$(grep '^fg=' ~/.glassrc | cut -d# -f2) | cut -d= -f2)
sed -i "s/^fg=.*/fg=$hex/" ~/.glassrc

To embed prism as a colour picker inside another TUI, use --out=FILE: prism draws on the terminal as usual, but writes the result to the file instead of stdout, so the host app's screen and prism's UI don't collide. The caller launches prism --pair --out=/tmp/pick $FG $BG, then reads the chosen colours from the file (this is how grid colours cells).

Keys

Footprint

• ~500 KB stripped binary
• ~5 MB resident
• Pure ANSI 24-bit truecolor, no kitty graphics dependency
• No subprocess spawns once running, no polling

Compatibility

Works in any terminal that handles 24-bit truecolor SGR escapes:

• glass, kitty, wezterm, foot, alacritty, st, xterm (with 256 + Tc), iTerm2, Apple Terminal (modern)
• tmux: requires set -g default-terminal "tmux-256color" and set -ag terminal-overrides ",xterm-256color:RGB" so SGR 38;2/48;2 passes through

Why "prism"

A prism splits white light into its component colors. The picker splits a single hex value into its R / G / B and H / S / V channels so you can dial each axis independently while watching the result on real text.

Part of Fe₂O₃

License

Unlicense (public domain). Borrow or steal whatever you want.