In Divinity the item colour was just a rough classification of its quality. The scale from low to high was; white, grey, blue, green, yellow, gold.
I believe this is the same in Beyond Divinity, but have not been paying much attention to the colours. I have found a white unique item, as well as a couple which were green.
There have been a few changes from Divinity's charm system (see
Locus Inn's Charm Guide).
from weakest to strongest;
Uru (green), Ser (blue), Min (red), Pag (silver), Yit (gold)
effects;
Umn - Vitality
Iceri - Mana
Ydra - Strength
Joph - Agility
Vorr - Constitution
Koor - Intelligence
Zand - Survival
Ook - Regeneration
Ustr - Evasion
Isos - Durability