because the flowers that were named for it, part of their shape looks like testicles so they say, but IMO they don't.
from wikipedia.org:
"Orchis is a genus in the orchid family (Orchidaceae). This genus gets its name from the Greek όρχις orchis, meaning "testicle", from the appearance of the paired subterranean tuberoids"
Orchid is also a color though, and doesn't have anything to do with the flowers.