viens are dark green the rest lighter

Hi,
I have just moved my babies from the trays to planting them in their final pots and they're the usual tall and spindly as it gets pretty crowded for them.
Anyway that is normal for me. My question is , they have been 1 week now and they are starting to get that nice darker green ( top leaves) like an indica does. But some are getting darker in the veins only. The rest of the leaves are way lighter.
I don't remember if that has happened before as I cut down feeding the babies for that last 2 weeks, Then after I plant I feed them.
Why are the ones getting green around the veins only. Are they lacking anything?
I could use someones help and suggestions,
Cheers

I just fertized with Pro Plant that I use normally of 20-20-20 and I will have to wait and see how tyhey react to it.
Here are some pictures. I read in another post that someone thought it was iron. Plant Prod has all of those minerals in it that are mentioned in some of the posts here.
Here are some pics. Unfortuneatley they are taken with a phone so they are not that clear but you will get the idea.
Some input would greatly be apprecaited!!

looks like a deficiency to me-possibly iron or mg-are you checking the run off ph? that soil may be acidic causing a lockout

the early stages of Mg def. Get yourself a box of Epsoms salt, and mix in 2 teaspoons into a spray bottle. Spray down your plants lightly with this, and wait a day, maybe even less. If you see improvement, then mix a batch into a gallon and water some epsoms in. If it doesnt improve the problem, then at least you didnt water the epsoms into the soil and possibly hurt your plants even more. Lightly misting them is all youll need to be able to tell if its an Mg def bro.

You can Google Marijuana deficiency to get some pics... I bought "Marijuana Horticulture:
The Indoor/Outdoor Medical Grower’s Bible by Jorge Cervante" the book has pics of deficiency's and def. a good read....... Bandit is right i get deficiency's when my PH is wack.....
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