you have multiple strains you say that do this? I am confused since your suggesting some gentic gene that does this which i do see being possible but if so it would be an anomaly in which case i highly doubt you have multiple plants with this same problem.
Not saying I am the greatest or even great for that matter just ok but i know enough to know you may want to try something new with those "genetic" 2 tone plants because odds are it's something you have done..or maybe i am a moron could be.
Ok, First off, this is NOT a problem! It is a genetic "thing". I have 2 strains that ALL the seeds that I popped had/have this "trait". I have seen this "trait" on at least 1 other strain not in my grows. It is NOT something anyone has "done" to the plant, except for the breeder who picked (somewhere along the line in breeding) plants that had the "trait" for his use in establishing the "new" strain. You must remember that in breeding you will express the "traits' of both the male and the female in the resulting "offspring". Breeders are attempting to express in the offspring the desired traits of each. One of the parents had this 2 tone trait in the breeding of this strain and in the end it turned out to be one of the dominate traits passed on to the offspring
of this strain.
So, that means that all the resulting offspring from the breeder then stabilizing the strain for "market uniformity" HAVE this 2 tone trait!
Like I said, "THE DOCTOR" strain from Green House seeds HAS this trait....Order some,,,,,see for yourself!
I could bore the shit out of you with technical terms and long winded explanations of breeding practice, but attempted to keep it short and simple.
If you still would like to learn about genetics?
Please read a book about the subject. There is a WHOLE lot more to KNOW, then just taking pollen from one and putting it on another to make a new one!