Yellow and purple leaves

[Lycopersica]

After watching the autumn leaves change outside, it seems my windowsill tomatoes decided to join in! Seriously though, is this a nutrient deficiency (nitrogen and/or phosphorus?) or some sort of disease? If it's a nutrient deficiency from being root-bound is there anything I can do aside from re-potting the plants? They're determinates near the end of fruiting so I'd rather not dig them up now.