white = weak hit (from affinity)

red = normal hit

blue (purple) = strong hit (from affinity)

yellow = critical hit

they're all different types of hits. white is a weak hit, only possible when the attacker has an affinity disadvantage. it deals less damage and cannot place debuffs. red is a normal hit. purple is a strong hit, only possible when the attacker has an affinity advantage and deals extra damage. yellow is a critical hit, which deals additional damage based on the crit damage stat. blue means the champion being attacked is under a shield buff. it's largely the same as a normal hit, except that effects life lifesteal and leech don't trigger from hitting shields.

Thanks Skadi & Carp_piscis

now i understand and can now judge damage appericate it

A good post.  Thanks for asking.