Well, I'd hesitate to call you colour blind since you are in fact correct. The dress really is blue and your brain is somehow undoing the mangling that's been done by the camera and lighting to arrive at the correct colour. I can't unsee it as white and gold however.
You can think of it all hinging on the blue/white stripes.
Objectively they're grey with a little blue in (check with a colour picker). All colour interpretation is ambiguous since you have do undo the effect of lighting and uneven colour sensors (eyes included). If your brain decides the light is white with a bit of blue, then that implies the underlying colour must be white and so the other colours must be gold.
If however your brain makes the call that it's strong orange light then that implies the stripes are in fact blue. That further implies the other stripes are dark grey, usually intrepreped as black.
There are other optical illusions designed to trigger this different intrepretation such as this:
http://en.wikipedia.org/wiki/F...
What's unique about this is it's not made to trigger two different intrepretations in one person, but instead by chance triggeres quite evenly the different intrepretations in different people, leading to big debates.
For you, the XKCD one isn't extreme enough to push you in different directions. Interestingly high level intrepretation has a big part. I can't cite anything but I can give a personal anecdote. The other day I saw an odd green thing on the floor in my hotel room. It was actually my backpack lit with green tinged light, but was crumpled in an odd shape so I couldn't tell what it was. When I figured it was my backpack, I could no longer see it as green (the actual colour is black). I probably spent 5 minutes staring at it trying to re-see the green with no success. It's a good illustration that the brain uses information from all levels including high level information such as recognising a specific object that I know is in the room to intrepret light colour.