Yellow Leaves?

I'm in the Los Angeles area and have a friend who is growing medically and I had bought him some seeds Skunk/Haze to grow outdoors. He currently has a few plants goin' but a few of them seem to have a yellowish color to the leaves...he's growin' them in descent sized pots with organic soil plus earthworm castings...because its so damn hot over here, would that be the concern with why they are discolored?? should he water more often or what?? and also specifically..one of the pots which is made of some rubbery/cardboard type material..the leaves are especially yellow on that plant...how can they be made more healthy?

There really is not much said on conditions other then heat...

Real quick one thing I found to worl miracles is Insta Green from Gro Tek.. $14.00 Ltr

If they are flowering I would not use High high Nitrogen...

If you really want to fix it we need all Nutes,PH,Strain,veg,Flower,ect...

IMO if they are in Veg and you want them green try that produst with in 2 days they change it is a Miracle Product IMO..;.

Good Luck To Your Friend;)