The name of the game is that you add the food grade colouring just before serving -- well an hour or so before -- BUT -- be very circumspect with how much you add! Most colour additives are extremely potent in colour terms.
If you add before bulk/bottle aging then there is likely to be a deterioration in the quality of the colour and goodness knows what effect it will have on the taste, long term.
I even make my own "Crème de Menthe" liqueur ( and several others and part of my process is where I marinate mint leaves in 40% abv vodka with good flavour extraction -- but there is virtually no colour extraction. I presume that chlorophyll just isn't green at what molecular level it all combines at. I do use food grade colours in my liqueur efforts and have never had any degradation in colour long term. Colour extraction for my strawberry liqueur is normally enough from the natural fruit without the use of colour additives.
As an experienced cook, at chef standard, I have frequently used food grade colourings to produce "special effects" without effecting the flavour of any particular dish. It is, however, quite amazing how strange colours effect the taste buds -- it's all in the mind!