Yellow is a color derived from the primary color red. Therefore it is a shade of red. When red is mixed with green, you get yellow. As you add more red, the yellow becomes orange. Eventually it turns back into red. If you mix red and blue you get purple. If you mix all three, you get black. Basic physics concerning the light spectrum. Didn't you play with paints in kindergarten?
And yes, if the yellow was separate from the green, it would be noticeable. But the whole idea is that the yellow is blended in with the green. As in it becomes a part of the green. So when you take away the blue to look for the yellow, all you find is the yellow that made up the green because like you said, green is yellow and blue. That means, before we even add blue, there is already some yellow. The yellow we are putting will mix in with yellow that is already there and become a part of the green. Do me a favor. Get some lime green paint. Put a drop of yellow. Stir it. And then take a picture and highlight where the yellow is. That is the whole concept behind this idea. The yellow we add to the green becomes a part of the green. To be honest I don't know how to explain this any simpler. I understood this stuff about colors when I was in kindergarten. Of course I was reading third grade-level books too so I might be the exception.
Look, I've noticed a pattern. You always ask a question. If it's not what you hear, you hide behind "Source! Give me a source! I'm not listening!" You asked why. Someone then asked how brainwashed recruits could even make it into the Chapter. We are giving you ideas. In fact, this sleeper personality is the only idea that has been presented. Obviously it works in the fluff because it has been done, not once, but twice. Maybe I should use the word "nascent" so it looks like it was straight out of the Codex. Now why doesn't it work on First Founding Chapters?
Why is the sky blue?(anyone who answers with physics behind this rhetorical question will be stared at with a look that could kill a basilisk)
Why does the sun come up?
Why does Cadia still stand with a single fortress on the ground and another Segmentum's battlefleet in orbit?
Why did the Necrons go from mindless machines to robots with personalities?
Why is the warp so bad?
says so. To actually destroy an entire First Founding Chapter would be so damaging to them it would not even be funny. Anyone who even thought of being a fan of that Chapter will be gone. Badly mauling a Chapter can instill motivation in fans, to help "rebuild" the Chapter by adding their own fluff to it. But kill it and it does. And out of the two Chapters that were infiltrated by the AL, both died. First Founding status would do nothing to change that. Except for the real-world reason just put up.
So to answer your original question as to why First Founding Chapters aren't infiltrated, it's because of the fans. They wouldn't like it very much. It would have a worse reaction than the Deus duology because there would be no new fans.
In summation, yellow is green when it is put into green because green is yellow and blue. The First Founding Chapters are safe not because they are super-awesome, not becausetheir Librarians scald the minds of aspirants looking for a drop of yellow in the color green, but because GW
doesn't want to lose money. There, you have an answer.
And I re-read the Long Games. It was only the last two batches of aspirants who were influenced. Those aspirants were either Scouts in the Tenth Company or were newer full-grown Space Marines in the Ninth. All command staff was still loyal and were executed. The First Company was destroyed in the Revenant Rex
, the Second and Fourth died at Phaetheon IV, the Third and Fifth died in the Damocles Gulf, the Sixth was jettisoned into space by the Tenth in orbit of Carcharias, the Seventh die defending the Fortress-Monastery and the Eigth were killed by the Black Legion in the Sarcus Sector.
Also, another thing that separates the Crimson Consuls from the Emperor's Swords other than the involvement of the Black Legion, is that the indoctrinated were supposed to commit suicide at the end of the operation.
My source for everything concerning the Crimson Consuls is pages 182 through 184 of the short story, Long Games at Carcharias
of the "Victories of the Space Marines" anthology.