You need drainage and I would tansplant into bigger pots (8inch aka one gallon pots), the purple is definately lack of nitrogen but this could be because of the soil conditions. I would not use 10-15-10 nute for that stage if you can't get equal measures i.e 10-10-10 or better 10-1-1 in nitrogen then don't use it. For seedling and vegging nitrogen has to be greater than or equal measure to P-K. This is vital.