Wonderful!
I love these foundation powders.  Customers service is amazing.  I sent a picture of myself via Facebook messenger and the owner Katherine and her staff members helped me pick my matches.  Mixing foundation shades is simple and so fun.
I am a medium dark skinned African American woman.  I learned that I have a yellow neutral tone that is slightly olive.  My perfect mixture is Xantha as my base color and Melanie mixed with a little Olivia.    For a darker more tanned looked I wear Xantha and Olivia alone.   I always apply Xantha to my skin first as a pre concealer foundation and to lighten and add more yellow to my foundations.  Then, I add Melanie alone, Olivia alone, or a mixture of Melanie and Olivia on top depending on the look I am going for.  
I have very oily skin.  I use the velvet formula.  A little goes a long way.  Coverage is excellent and the formula is gentle and does not break me out.   I apply my foundations dry, using the wet method, or simply set it with distilled water depending on the look I want.  It is versatile.   Thank you for these nice products and great customer service Sterling Minerals.