Food identification in fajitas - yellow sauce I'm looking for the name of a yellow/ochre colored sauce, used in fajitas among other things. I've been to a tiny Mexican restaurant a couple of times and in there the guy made his fajitas with such a sauce.

Now, I know that description isn't worth much, but I was hoping somebody could help me nonetheless. I can't really ask him, since I don't know his contact information, plus his shop isn't exactly close either. The shop is pretty small and it's in West Europe, so it may or may not be 'authentic' Mexican cuisine.
This does not sound like a traditional fajita sauce. The yellow color is likely to be from achiote (annatto), which is widely used in Mexico. It has a mild peppery taste, but is used more for color than for flavor.