i've seen a drk grey horse out competing before and the rider had on some light blue and pink, suited him very nicely indeed but i think a white would go well with you also ! xx
i've seen people in all sorts of dark greys... they are a lucky colour because most colours look good! i would agree with LBertie Wooster about light blue and pink looking nice on greys... xx
We have a lovely grey mare, who has sadly gone lighter! As other posts have said, you can get away with any colour. As we do western, we've played with colours for saddle pads and shirts a lot. Purple looks fab, as does turquoise and even lime green. Avoid black, white, and TBH I would say navy, and be creative!