My childhood friend of 17 years is white. We were childhood friends since the age of 6 where we met in our neighborhood (which was mostly white). She grew up in a bad situation and was on her own from the age of 14, while I grew up in a solid, loving family which adopted her on some level. She moved constantly because of instability in her life but always kept in touch with me and made it a point to keep me in her life.
We don't have too much in common in terms of music, clothing, activities etc. but she knows more about me and would do more for me than anyone (besides my family) and we shared most of our life and memories together. We share big things though such as world views and religious/spiritual outlook.
I would call her my oldest closest friend, and my best friend who's mixed would be the friend that I share things in common with and speak more with on a daily basis.

I never talk to her (the white friend) about race. I can't feel comfortable sharing that with her and I don't think she would understand, but I share that with my mixed friend and because of that I have a different kind of closeness with him that I won't ever have with her.