Logical Angels on Christmas Tree

How their logical skills are challenged?

Case 1 :

The angel A observes that the aureoles of B and C are of the same color. Then, A can be sure that the color of own aureoles must be other than that of B and C.

So, A will be the first to guess the correct color in case he observes 2 same colored aureoles B and C.

Case 2 :

The angle D notices that the color of aureoles of B and C are different. Now, A has to remain silent. The silence of A suggests B that the color of aureole of B must be different than the C.

So, in that case, B will be the first one to guess correct color of own aureole.

However, C has no chance to guess the color of own aureole unless, A or B reveals color of own aureole. And D has absolutely no chance of correct guessing the color of own aureole.