I have two different lemon balms, a variegated one (Melissa officinalis 'Aurea') and the standard one, which in my garden gets giant leaves, but that's another story. I find that new growth on the Aurea does have a purple 'cast' to it when its first growing in the Spring and it tends to look glossy for the first few weeks. As it grows taller, it looks how its supposed to. Not sure why this happens but it tends to be worse when we've had a colder winter? Not seen any new aurea in the garden so far, but I haven't been looking, will have a look tomorrow and see if it has purple bits this year, if it does I'll take a photo and we can compare. Mind you you may not have Aurea...?
It is good to get out and do stuff, all being well I'll be getting some seed sowing done this weekend, just got some new herbs that need to go in the greenhouse until things warm up a bit, but there is promise in the air and the scent of fresh herb tea isn't so far away now