I just went to someone's blog and found this interesting information:

Why transition metals compounds are coloured?
In the presence of ligands (an ion or compound which has at least a lone pair of electron to donate to the central atom/ion), 3d orbitals of the transition metal ion become non-degenerate and split into 2 groups with slightly different energyWhen a d-electron at a lower energy group is promoted to a higher energy group, the radiation in the visible region of electromagnetic spectrum is absorbed. The light energy not absorbed will be seen as the colour of complex.

wow! such a very "chim" chemistry explanation(cuz i dun do chemistry in my course,but chem engrg ; except that i am currently taking a CLS common module basic instrumental analysis,BIA analytical chemistry)...well i am so sorry if i have copied this part of ur blog without ur consent....lol...the reason why i am copying this part coz not only for my interest(chemistry rocks!!!), but also to answer one of my friend's doubt..she's in DCP(chemical process technolgy),industrial chemistry option...yup...enough said...gtg do research for that horrible heat transfer practical(lecturer in charge: Ms ST phua,cP,u noe why le...) this coming thursday...sianz...aniwae,me just wanna wish this particular person, whom i copied the above info from,wanna wish her the best for the rest of her 'A' level paper until this friday(end)...加油!!! i will pray for u de!!!!