A few weeks ago, I got some haching eggs to test out if my constantly broody silkie would be a good mama hen. One of the eggs was a houdan and three of the eggs were easter eggers. The silkie has been faithly sitting on the eggs for 18 days now (fingers crossed). To distract myself from the waiting, I had to ask: what are the odds a chick (assuming a hen) would also lay a colored egg?
There are several different egg color genes, the wild white color, a blue color (dominate to white), a brown egg color (which is controlled by several genes), and a pink egg color. A dominate gene means if that gene is present, you can't tell the other gene is there (it is not expressed). A co-dominate gene means both genes will show (be expressed). The blue and brown are both dominate to white, but co-dominate to each other. If a hen has a white gene and a blue gene, she will lay blue eggs. If a hen has a white gene and brown gene, she will lay a brown egg. If a hen has a blue gene and a brown gene, she will lay an olive colored egg (blue and brown combined). This is because blue is the color of the egg shell, but brown is an overlay to the egg shell. A person can scrub the brown off an egg, but the blue eggs are blue even on the inside of the shell.
The most likely scenario is the rooster has at least one copy of the blue gene and the hen definitely has at least one copy (she laid a colored egg). So, if each had a copy of the blue gene and a copy of the white gene, 25% of their chicks would lay white eggs and 75% would lay a colored egg. So if there were four chicks, three would lay blue eggs and one would lay white eggs. (Keep in mind this isn't strictly true. If a person hatched hundreds of eggs, then these numbers would be right, but for small numbers of eggs like 3 or 4, a person could have all white eggs or all blue, who knows.)
The best case senario is that either the rooster or the hen has two blue genes. In that case, 100% of the chicks would lay blue eggs.
Worst case is the rooster had two copies of the white gene and the hen had one copy of the white gene and one copy of the blue gene. At that point, 50% would lay white eggs and 50% would lay blue eggs.
Now an interesting thought is what if the rooster had a copy of the brown egg gene? If the rooster had two copies of the brown egg gene and the hen 2 copies of the blue egg gene, then all would be olive eggers. If the rooster had one copy of the brown gene and one copy of the white gene and the hen had one copy of the blue gene and one copy of the white gene, then 25% would lay white eggs, 25% would lay blue eggs, 25% would lay brown eggs, and 25% would lay olive colored eggs. So, 50% of the chicks would lay a cool colored egg of some kind.