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.
I'm not loving this really; can we switch to a class on the div, slurp in a css file and put 
`border:2px solid #999;height:30px;width:30px;margin:5px;margin-right:10px;margin-top:3px;float:left;` in that for it?