Never heard of using milk and I'm pretty sure syrup would not have the same exact effect, it might work but likely not as effectively.
Also dropping your temperatures at night will enduce your colour changes in your bud.. I am interested in knowing what else is good for bringing out the flavours though. The current girls I have are purple lemon skunk and when I grew them last time in bad conditions they had such a purple taste(if that makes sense to you). Great strain for outdoors as it produces a lot, very vigorous and I've never once burned them even when I don't measure my mix... Sadly for you all it's a personal strain of two types of bagseed
One batch was purple star and one batch was lemon skunk.. Forgot about a batch outdoors till late one year and when I can back I had 4 plants that were just under 8ft full of seeds because of one lemon skunk male