Who's painting anything? The link clearly shows horses covered in blankets. I'd imagine the comparison is done only between horses covered in blankets of various patterns, so the pattern is the only significant variable.
I confused it with different experiment when they directly painted cow (AFAIR) and measured number of mosquitos.
Yes, here with all blankets of equal size it seems to provide more relevant results about which pattern attracts insects, though not sure why they didnt test zebra stripes which they keep mentioning.
