Blue and brown make what color?

It depends on which blue and which brown you use. There are a wide variety. For example if you mix ulra marine blue and burnt umber you will get black. Adding blue to a reddish brown will make the brown darker, but also more violet. Using a yellowish brown and blue will give you more of a greenish brown.

You have to experiment with the colors on your pallet to see exactly which one you get.

The related link below will help you understand more about mixing colors to get the ones you want.