Consider supporting arbitrary color schemes

[andymatuschak]

Orbit prompts have a color associated with their source. Authors currently choose that color from a limited palette. Some authors have expressed interest in choosing arbitrary colors. We should consider supporting this.

Some reasons why this is not totally straightforward:

• Orbit's palettes are not a single color but a set of five colors hand-chosen in association: a background color; an accent (usually complementary, but with a lot of hand-tuning); a secondary accent (usually analogous, but again with a lot of hand-tuning); a secondary background color (a shade, often also manipulating the hue to avoid losing too much value); and a secondary text color (a more straightforward shade). How to choose associated colors for a given input? What should we do if we are given a grayscale color? Do we just insist that the author choose all five? That sounds like a recipe for disaster. More likely we'll need to fall back on some computational scheme.

• The color palettes are chosen to maintain a coherent art direction in a review session which spans many sites. You might have quite a kaleidoscopic review session, with the prompts changing color after each response, but this isn't jarring because they're all drawn from the same retrofuturistic tonal palette. If we allow arbitrary colors, multi-site review sessions will likely feel much more garish. Separately (and perhaps less importantly), the art direction will be diluted.

Noting: PJ has requested that we do this!