I just associate them with the colour spectrum, sice it looks nice on a char sheet:
STR - red
CON - orange
DEX - yellow
WIS - green
INT - blue
CHA - violet
Note, that I changed the order of the stats.
What is interesting to me, is that I'd always use 'warm' colours (red, orange, yellow) for the physical stats (STR, DEX, CON) and 'cold' colours (green, blue, violet) for the mental stats (INT, WIS, CHA).
It makes sense to associate physical stats with combat, exercise, heat, warmth and thus reddish colours. Just like associating mental stats with rationality and calm.
My list:
STR: Red
DEX: Yellow/Green
CON: Brown
INT: Blue
WIS: White
CHA: Purple/Pink