Something that I do these days before adding a piece, if I'm worried about clashing, is going through 1-2 weeks of normal life (in the clothing/outfits you would typically wear for whatever those days bring) and thinking about which choice you would reach/would have reached for that day. If you get through the time period and realize you would have reached for Onyx the most, that's probably a safe decision. If you end up wishing you could have reached for a pop of color for most of the days, that may be your choice!