The other good tip is, once you find a colour that suits, hold onto the dregs, and take it with you when you go to choose a foundation. This will help you to be able to colour match.
Great tip! I do that too. I got a Clarins foundation one time that was the perfect colour, but I just didn't have the finances to keep buying the expensive brand, so I took it into a department store and found a cheaper brand with a colour that was almost identical. I actually use them for different purposes because the way they cover is very different. For every day use I use the cheaper one mixed into some moisturiser. It's a very silky foundation and is easy to apply and blend evenly. The Clarins one is a little thicker and seems to dry and be absorbed on my skin quicker, so even when I mix it with moisturiser I have to apply it faster or it will be uneven. Having said that, it gives better coverage and looks better, so I use that one for special occasions.