Try as I may, I still have not found a recipe to beat this one, the only problem is its impossible to keep the brilliant mint green colour, its just one of those things. Vinegar destroys chlorophyll, (the green bit in plants) very quickly indeed.
The only way around this problem is to make the sauce or jelly, cool, then strain or sieve out the discoloured mint. Chop a fresh batch and add. It’s all a bit of a palaver, and the whole point is that it will discolour again pretty quickly, so, I just don’t bother.