Go for the science here, please. Do some research on synesthesia. This is NOT an affliction or a disease but simply the way some folks see the world due to their brain wiring: Letters can have colors, musical notes can have colors too, or words or music can have "flavors" people experience. It is caused (scientists believe) in brains where certain areas for processing language and areas for color etc. fire off so close to each other that they mingle, so words have colors. But there are other manifestations. Rent the episode of the PBS NovaScienceNow series about how brains work, to learn more.
She may or may not be a synesthete but if she is there is nothing wrong with it or with her -- in fact, she is going to see the world in wonderful ways. On the other hand she may simply be very sensitive to color, or much more imaginative than you realize!
The angels thing is likely her way to cope with deaths. It is very typical for young children to believe they can hear or talk to the dead and it helps them feel in control. Don't discourage her. I do not think it is related to the colors.