How To Cure Purple Discoloration In Left Foot Due To Dermatitis?

Recently I experienced a staph infection which manifested itself visibly with sores on my feet which a dermatologist labeled contact dermatitis. I took a sulfa drug and doxycycline. Feet cleared up but they still swell a bit when I'm on them a lot, and my left foot is still quite purple. How long does it take for the purpleness to go away/