ColorCodes: simplify and comment a bit.

- Simplify logic and increase explanation to make it easier
  for the casual reader.
- Remove the undocumented, untested and not-clearly-working
  "percentage" support.
- Replace `eval` with `try`, as is my wont.

Addresses #620.
ColorCodes: allow for rgb #123456-style queries
ColorCodes: rough in a different HTML template.

Real templates are coming, but this is a step.
Merge pull request #625 from mwmiller/color_sanity

ColorCodes: simplify and comment a bit.