Some years back I read in a flying magazine that they did a test on color to be seen from every angle and elevation.  A light bright orange was the  color they choose as the winner. Personally I think yellow would work well. Doug Wheeldryer who used to work for Lancair had a 360 painted yellow and you could see it  very easily over the others when he raced it during the annual Labor day fun race they hold each year.

                                                                             Gary Trenner 360  40% ?