from what i can tell, its the second rank of an enchant that gives a glow if it has multiple ranks. intellect, spirit and damage are the 3 that glow upon rank 2. beastslaying seems to be the exception but with there being beastslaying +6 and elemental being +6 only (thats the only rank), beastslaying +2 seems to be one of the enchants that probably shouldnt be there or they couldnt be bothered to put in more elemental slaying (kinda like absorption on chest, stupid enchants)
spell power and healing power are purple.
strength and agility are green.
spirit and intellect are yellow.
crusader and icy chill are white but icy chill is far brighter white.
demonslaying is orange.
fiery is orangey red.
elemental and beastslaying are both red.
unholy is 2 glowing green skulls revolving around the weapon.
lifestealing is purple.
+damage is blue. the more +damage (i.e. the higher rank) the thicker the glow becomes
black is for the top end AV rewards, comes with the weapon and cannot be over-written with another glow. same for the Qual'serrar, natural green that cannot be over-written.
as of yet, there is no black enchant, it comes with the unstoppable force or the lobotomizer
wrote that on another thread a while back so there ya go, theres the comprehensive list. as an enchanter, i know theyre correct. Torux was correct on most but crusader is wrong- its white like icy chill, just not as bright. you probably saw a crusader on Quel'Serrar and just got mixed up