If a hen has red earlobes, usually she will lay brown eggs.
If a hen has white earlobes, she should lay white.
Some crosses will lay colours. My Leghorn mix lays pink tinged eggs. And my Brahma mix laid a baby yellow egg.
You can tell most of the time from the color of the legs, but it doesnt always work. Hens with orange/yellow legs are usually from the American class and lay brown eggs. Hens with white/pink legs are often from the European class which lay white eggs. Ameraucanas have green legs and lay green or blue eggs. There is a lot of overlap so you can't always tell unless you know the name of the breeds.