From White to Brown -- Is it possible???

I have 7 game hens that were laying white eggs, well since my other 8 hens (RIR, PR, WR, BO) have started laying the brown eggs -- all my eggs are brown. I see my games sitting in boxes, singing the egg song -- all the evidence I need to know they have laid an egg. but they are all brown now. Is it possible for them to "switch" color? Or, have they just stopped laying all together or laying somewhere else...