I can only draw on my own limited experience but with my two batches of home reared chicks coming into POL the coloured egg layers have always started laying properly coloured eggs straight away (Cream Legbars (blue) and Barnvelders (darkish brown). It seems to be more the shape of the eggs that needs a bit of practice to come right, the first few eggs always seem on the small side, and I had a couple of shell-less eggs too.