I can't help you with the purple coloring unless you get a pic. Some gold gouramies do have purple-blue markings but not necessarily concentrated around a particular area.
Gold gouramies are one color morph of the three-spot gourami, Trichogaster trichopterus. Other color morphs include blue, opaline, cosby, lavender and platinum. They are one of the most aggressive gourami species so the behaviour you are describing is to be expected.
What sexes are yours?
It is never a good idea to keep this species in pairs. The more dominant fish will tend to bully the other and can cause it severe stress. Two males will readily fight to the death over territory.
How large is your tank?
They grow to around 6" maximum - how large are yours? They may mature at half that size so yours may well have reached sexual maturity and are starting to become increasingly territorial and competitve. If you have a male/female pair, one or both may be becoming interested in spawning. Note that, if they do breed, the male can become extremely aggressive and may well attack and kill even non-gourami tankmates whilst guarding his bubblenest.