is this a problem?

i have 3 plants , 2 skunk #1 and a top 44 and they have been in flowering for 19 days and recently the veins on some of the older leaves are turning a very light green but the leaves look very healthy so i was wondering if anyone knew if this was a problem or normal.

Post some pics . That would make it alot easier to help you

sorry i posted pics in another thread but i cant get a good close up on the veins but after looking at them for a couple days it doesnt look too unnormal but thanks for the post man.