Optimise admin css colors

[thomask]

It is really pain to create own admin color pallete, as the current ones are too complex. E.g. in current colors-fresh.css you are using circa 90 colors, many of them almost identical so noone can see the difference (especially when they are on different pages, places) and you are also using different naming conventions

6hexa #666666

3hexa #666

color name black

and also different case in hexa e.g. #FFFBCC vs. #f1f1f1

IMO the default number of different colors could be decreased to about half without visible concerns and also standardising naming convention would help for creating own themes

Actually, there are some standards - just need to work on following them :)

"Use hex code for colors. Avoid RBG and uppercase, and shorten values when possible: #fff instead of #FFFFFF."
-- ​http://codex.wordpress.org/CSS_Coding_Standards

Related: #20570