I'm really curious
and sorry for cluttering up the thread, but since you've traveled before and knew you were going to a remote area, why don't you have your little energency medical kit with you? I know weight in luggage is an issue, but for myself, I'd give up something else before I'd give up my emergency medical supplies, especially on a trip like yours.
Also, I may have missed this, but why does it look black? Is that blood under the skin like a blood blister?
The Chairman kept going on about socks. The absolute best piece of kit that I've ever been blessed to have been told about and then purchased asap, is lycra dive socks.
First, I don't dive without my socks on. Second, if I had a wound on my foot, I'd do as uncfnp said. Plus, for the dives, I'd have it bandaged within an inch of its life after I'd smeared it with Polysporin Complete (3 antibiotics and pain relief).
I had a wound on my leg when I was in Bali last winter. Kept it clean and washed well before and after diving. Kept it covered. I was getting nervous as it was becoming more red around the wound site and I thought that it might be getting bigger too (imagination?) It was infected but I kept at it. Eventually, my return to Singapore helped to clear it up.
Regardless, if you've got a few days that you don't mind keeping it out of the water, then that's probably best. But, as you are aware, there's still "stuff" everywhere especially near a toe!
Any other tourist divers around? They might be willing to share their emergency supplies. Don't be shy.
Best of luck with it.