Well, what I did was ask the assistant! Or rather my friend did. I was makeup shopping in boy mode, with an out trans woman friend along for moral support. My friend just said to the assistant, "Excuse me, miss, my friend here needs the works." The sales lady then selected colours for me that matched my skin tones.
Apparently, the best place to check your skin colour for matching a foundation is the inside of the lower arm. It seems to work pretty well on my face. I'm not sure how she came up with lipstick and blush colours, but the combination works, so she must have known what she was doing.
I'm actually planning to go for a consultation soon. So I'll get another opinion, and maybe a better product line. But I've been happy with the first person's colour choices.