Are light green leaves always sign of a problem? (pics)

I have a bunch of plants nearly a month old. Recently when I potted up I ran out of FF and decided to make Blazeoneup's soil recipe. These guys received Blaze's soil and they both look quite strong and healthy except we have these light green leaves coming in now are different from what I've seen so far.

I give them the same water in the same amount as my other plants that have not experienced this. I haven't given them nutes so far either.

You can see the contrast in color between the top and lower leaves...

As I said, with the exception of this color, everything about them looks great. Should I be concerned?

Sometimes new growth will be lighter. Just monitor the leaves for any signs of nitrogen deficiency.

That looks perfectly normal to me...just like mine looked.

They look healthy, probably should start them on some nitrogen.