Though the jewish community gets most of the sympathy for the holocaust, they werent the only ones in the camps. Most of these people were given a symbol of identification, coloured triangles. Some of these symbols went on to represent the group of people after the holocaust (homosexuals, for example)
Red: Political prisoner, often a communist or socialist that is not a nazi.
Brown: Sometimes used for undesirables or antisocials (like non-comformists) instead of black triangle, which was sometimes reserved for lesbians.
Purple: Jehova's whitness
Yellow: Jew, 2 triangles used to form a star of david, this second star can be combined with any of the other triangles to form the star if they happen to be jewish too.
I felt like doing something informative, so here it is.