Linkerd2: change css variables for color to be more descriptive

[franziskagoltz]

currently some of the variables in css representing a color are named:
--latency-p99; --latency-p95; --latency-p50

it would be great to change the naming to be descriptive of the variables representing colors, as is done with other variable names.

[rmars]

Suggestion: we use something like http://chir.ag/projects/name-that-color/#56CCF2 to help us get a human readable, descriptive color name for each color.

[rmars]

(name that color still won't produce a unique name for every hex color, but it does help, and probably gets us most of the way)

[rmars]

Fixed by https://github.com/runconduit/conduit/pull/147