Yellow as in yellow new growth-- or yellow as in dry/burnt??
They may NOT be as far along as you think-- Flower doesn't start day one of 12/12-- but the 1st day the plants actually start to flower, anywhere from a few days to 3 weeks after going into 12/12... around week 4-5 of flower, many plants start getting deficiencies-- best dealt with by flushing the plant- then waiting a couple days and feeding it... with "transition" nutes... follow a feeding schedule for the nutes you use... only way to really stay on track!
edit/note: people online will not Email a stranger asking for technically 'illegal' advice... especially to someone with the name "Convicted One".... Emails are traceable, and people in this "hobby" (if smart) Try to stay off the radar.... Stick to the boards, or even PM's within the site...