Paint? Will paint work? Maybe, but I didn't think it would.
55 degrees is pretty cool.. it might take days to set up, I guess it would
depend on how thick. Thinner castings don't hold heat as well, so they take
more catalyst to cure. The catalyst generates the heat needed for curing,
but that might just be too cool for even 5 drops per ounce. Especially for a
flat, thin cast. (don't know what you cast ,so I'm not saying that is it)
Any chance of getting your casting someplace warmer? Like a toaster oven?
I'm still not sure about the paint, though. Most everyone recommends their
own particular pigments for coloring, and even pigments for some products
will stop a different product from curing.