In hex you use three or six digits to define a color. By replacing all six-digit colors with the closest color which can be expressed with three digits, we save 3 bytes each! Hooray!
http://www.w3.org/TR/CSS2/syndata.html#value-def-color
The three-digit RGB notation (#rgb) is converted into six-digit form (#rrggbb) by replicating digits, not by adding zeros.
Examples:
'00ff00' -> '0f0'
'34cf9d' -> '3c9'
The idea was to have a meta function which finds all
/#([0-9a-f]{6})/i
inside the CSS file and passes it to this function. Could then be used in stuff like CSS minifiers as an option (because it's destructive).This could of course all fit in 140 bytes combined ;-)