All and all they look good. Nothing a little adjusting cant help.
Do you have a ppm meter?
If not - Maybe change your rez and go 2/3 of the recommended strength and see what they do. Those spots will not turn green again, but it would be a good idea to avoid your new growth having this issue also. It is most likely stunting their growth at the least. I had some of my plants form similar spots on them after I changed the nutes from veg to preflower - I knew I mixed it strong and confirmed with the ppm tester, but I didnt add water like maybe I should have. I kept an eye on them, pulled a leaf or two off each plant, and they settled down, prolly got a little accustom to it with the lights at 12/12.