acid16

It makes color schemes. Pass a background color, an accent color, and optionally a foreground text color, and out comes a color scheme.

The program uses a quasi-HCL color model (see “The color model itself”). Color arguments are in the form of “hue,chroma,luminance” for background and “hue,chroma” for the other two. All values must be numbers between 0.0 and 1.0 (you're welcome to try other values, just don't be shocked if it breaks). Also, keep in mind luminance here is relative luminance, or the color's brightness as perceived by the human eye. So pure yellow has more luminance than pure blue. It also uses linear color ramping instead of the usual gamma-encoded sRGB, so something like “0.0,0.0,0.25” won't get you the #404040 you'd expect. This can be overridden by passing --hsl, that way you can use a good old HSL color straight from your color picker.

The script will do its best to make sure everything is readable. With Base16, for instance, it tries to keep a contrast ratio of 7:1 between the foreground and background colors, while trying to stay above 4.5:1 for foreground and highlight, the last 8 colors (the “hues”) and highlight, and the “dark” foreground and background. Usually it does a good job. But with the way it handles contrast, things get unreadable with some values (see “On luminance options”).

Example

./acid16.py 0.6,0.25,0.005 0.6,0.5 0.0,0.0

This creates a color scheme with:

• A dark bluish background (hue 0.6, chroma 0.25, luminance 0.005)
• An accent color with that same hue but more saturation (hue 0.6, chroma 0.5)
• Some shade of gray for the foreground color (hue 0.0, chroma 0.0). In this case it'll be a light gray since the background is dark.

Here's the preview it'd generate:

Prerequisites

• Python 3
• Pillow

Options

Obligatory “options are subject to change” courtesy warning

• -a author: Set the author name.
• -b amount: Make the hue colors blend with the color specified by -B. 0.0 (default) means no blending, 1.0 makes them the same exact color. If you'd like to have them be the same hue but with different brightnesses, use a value like 0.999.
• -B target: What color to blend the hues with: background (default), foreground, accent.
• -c contrast: Desired contrast ratio between the foreground and background colors. Default is 7. 21 guarantees the highest possible contrast (i.e. the foreground will either be white or black).
• -e: Equiluminant mode; uses the same luminance for the hues. This keeps their brightness uniform but can make them harder to tell apart.
• --hsl: Treat the background color as being gamma-encoded HSL (i.e. what most people are used to). Wouldn't recommend it, but if it works for you...
• -m mode: Which generator to use. Current generators:
  • base16 (default): Base16
  • xresources: Xresources terminal colors
• -n name: Set the scheme name.
• -p: Generate a preview image demonstrating color contrast and the palette itself.
• Base16 options:
  • -l: Don't darken the last color (brown).

Notes

On luminance options

The only good ranges for background luminance at the moment are 0.00 to 0.10 and 0.31 to 1.00. It's at these ranges that the script can maintain its contrast levels; anything between 0.11 to 0.30, and the foreground color will start losing contrast with the background. In addition, the contrast with the hues break down the closer you get to 0.30.

tl;dr: Don't set the background luminance between (0.10, 0.30] unless you like eyesores.

The color model itself

It's not HSL, it's not HSV, or LCH, or HCL, or really any of it (or maybe it is, but I'm not color-theory-literate enough to know). If anything it's basically HSL except with these changes:

1. Linear color ramping instead of sRGB gamma encoding. Internally this doesn't matter until it's time to actually display the color.
2. Whereas HSL gives you the pure color at 100% S and 50% L (and starts to blend it with white as you drive L up from there), this model gives you the pure color at a luminance dependent on the hue itself. So for instance, pure red (RGB 100%, 0%, 0%; or HSL 0°, 100%, 50%) has a luminance of about 0.2126. The equivalent in acid16's model is 0.0,1.0,0.2126. As you raise luminance past that value, the color will approach white.