Get their free sample kit first (includes your choice of 3 foundations, 1 concealer, 1 blush). As long as you have some idea about your skin color, like if it's a more pinkish tone or olive, etc. it won't be difficult to find the right shade. There's also a guideline on the website. And since mineral makeup is essentially powder, you can mix and match until you get the shade you want (which is why they give you 3 foundations!).

I'm asian with lightly tanned skin and pinkish / peachy undertones, and I wear medium beige.

Hope this helps!