If it is not colouring with light intensity, I doubt nitrate limitation matters. In theory, I would say why not, but in practice, with 'neglected' plant only tanks, I've never witnessed colouring under very low / no dedicated aquarium light.
Light intensity does make CO2 and O2 stress very pronounced. If you are able to help plants deal with this, you can crank up the intensity and induce pigmentation, without making the life of our marginal and marsh plants in fully submersed conditions harder than it already is.
Plants in good conditions are probably also much better capable of defensive biochemical warfare and perhaps managing the composition of epiphytic biofilm overall. Hence, (healthy) plant density matters to discourage algal spores from germinating.
Reducing the organics with water changes and maximising O2 to its soluble levels (in scope of organic break down), should help prevent germination also. I'd aerate tanks heavily at night to cause extra water movement and agitate the water surface, and allow water temperature to (naturally) drop, in the hopes to maximise O2.