Dog's tooth violets are Erythronium dens-canis - not true violets at all. As you can see from the many pictures returned by the google search below, the flowers are purple, not yellow. There are other species of Erythronium which *do* have yellow flowers, and indeed trout lily is one of these (E. americanum); that is the source of your confusion, methinks.

I didn't know Erythronium were edible until today, whence I find corroborating info on the Internet. Well what do you know?

Alternatively, though less likely, you might really be referring to dog violets. That name could refer to one of several species of true violet, all of which would be edible, though with minor reservations as regards quantity, cooking, etc.

Here is a link that might be useful: Dog's tooth violets images via Google