Silk Naturals

I am hoping some of you ladies can steer me in the right direction to create a foundation shade for my sister to try. She is Caucasian with a medium-dark skin tone, dark brown hair with reddish highlights, and very dark brown (almost black) eyes. She gets tan just thinking about the sun and never burns. We can't figure out what undertone she is, except that she is not yellow or golden. So I am thinking she may be a mix of things. I am sorry I don't have a picture.

Anyway if some of you darker-skinned, neutral-toned women could share or recommend a formula for her to try, I'd really appreciate it! I have all the dark bases I need to mix any color. I'd like to mix her something that is close enough for her to tweak by herself if she needs to.

Thanks in advance for your help!

I am thinking Ebony or Peach. I am colored like her, but very much paler (more a product of tha fact that I am inside all the time and live in a northern US climate). I always thought I was somewhere between Warm and Ebony, but Peach matches me the best. I will also warn you that Peach runs darker than the others (except Deep Ebony). Start at 1:4 in Peach and go from there if she is a med. to dark. In Ebony start at about a 1:1.