Can calico kittens be born Yellow/White and then the "Black" come the next day?

We had 2 kittens born yesterday, (1 black/white, 1 yellow/white), Today, we went out to check on them and we now have 1 black/white, and 1 black/yellow/white (calico). We are wondering how this happened? Are calico kittens born yellow and then get their color the next day?