The Rockwool solution has PH 5,2 EC 0,4.
After one day of diving solution has PH 6,4 and EC 0,5... so wrung out the rockwool cube and sowed.
After 3 day the plant sprouts from the cube.
Normal...not quite but definitely not a problem my friend. It's just a pigment mutation.
If you look at my lilac diesel diary you'll see she has quite the case of it as well.
Some plants grow out of it. Some don't. It's definitely not your light.
Hope this helps.