Is colour perception trainable?
If you ask a doctor he will say no it is not trainable it is inherited from your maternal grandfather. However, there is evidence that colour perceptions can at least be improved dependig on what kind of colour perception problem you have. If you do not have the cone cell required for seeing a particular colour then it can't be trained. If you have only mild red-green perception difficulty then it can probably be imporved by training.
People working in inductries where colour matching is critical learn how to judge colours in ever finer and finer nuances by practice / training. Colour printing, paint manufacturing, cosmetics, carpet making etc.
The Vision Training approach to colour perception deficiency in the common red/green spectrum is to encourage finer and finer differentiation of the problems colours. The training consists of exercises using colours so a deeper understanding of how colour work come about. Colour percption is about developing more and more reference experiences with colours in the range where difficulties occur.