Given I have an alpha blank/white, and two substituted black/black sigs, I'd discourage black/black or white/white or transparent/transparent.
I do find the clash visually, even to other people when they see the transition of black white very distracting. I wear my b/w alpha on my thumb and if it happens to slip around from its usable position, which is basically chip side down inner and other thumb edge, The transparent looks good, with the black being very constrasting/distracting - more so that the silver on my alpha.