Deduplicate colors that are aliases, e.g., "gray" and "grey".

[erictheise]

The scratchpad doesn't filter out colors that have multiple names. These include the numerous variants involving gray and grey as well as fuchsia/magenta and aqua/cyan.

One approach would be to manually delete duplicates from colors.js. Another would be to test against a known list of duplicates when assembling the array in distance.js.

At some point it may be useful to filter colors by which version of the CSS spec they appeared in and a brute force manual deletion would complicate that.

Working from the MDN list.