dot 5 is purple.
dot 3 & 4 are light amber[ish] in color.
i wouldn't put 5 in if you suspect it truly isn't purple color.
as to 3 & 4, i would just add some 4.
if a true color can NOT be determined, to be on the safe side, i would drain, flush with alcohol, then fill with your choice of fluid.
also, don't confuse dot 5 with dot 5.1. 5 is silicon [?] based, while 5.1 is not. also, i do not know what color 5.1 is, although i suspect it may be close to the color of 3 & 4.