What makes eyes different colours?

Eye colour - what a baby is going to look like depends on the 46 genes in his body cells. Half of these genes he inherits from his mother, and half from his father. Some of these genes determine his eye colour. All eyes contain blue cells, but some people have other coloured cells as well so that their eyes look green or grey or brown or hazel. Babies all have blue eyes because the other cells, if there are any, do not grow until the baby is about two. Sometimes people have eyes which are partly blue and partly brown or green. This is because half their eye has only the usual blue colour, while the other half has some other colour as well. When two blue eyed people have a baby only blue cell genes are being passed on, so all their babies will have blue eyes. But when one parent has brown eyes, a mixture of blue and brown eyes is being inherited, and the colour of the babies eyes will depend on whether there are enough brown genes to dominate the blue ones. Even two brown eyed parents may not have enough brown genes between them to have a brown eyed baby.