You've missed the point... the question is NOT "Give me an example of something that is liikely to be blue". Sure RGB=[0,0,255] on a standard commercial display device, viewing with a wide range of background conditions and lighting is very likely to appear blue to a normal observer.
But that is not real life and RGB only exists in the confines of a display device, not the real world where can have almost limitless levels of light energies of all different wavelengths and spectral signatures. Even in RGB space, could you reliably tell me whether a pixel in a visual scene that has values [100,100,120] will appear to be blue or bluish? NO YOU CANNOT.
The question of "is there a quantitative BLUE" is instead the question of "Is there a quantitative description of what about the physics of a visual scene (or light stimulus) that will ALWAYS appear to be BLUE, and DEFINES what blue is"... there IS NOT, certainly not a simple one, though we can come up with approximations based on physiology and psychphysics.
but fairly unlikely, at least not in the way you describe, with a "specific command sequence". 1) its at too low a level to be really useful as a backdoor, not without the help of backdoor software higher up, but then what's the point? there are already many "backdoor"-like ways to gain privileges as long as the software is there to support them, 2) it would have to be designed to NOT slow the CPU down or take up obvious chip real estate... the CPU biz is so competitive that any extra overhead of either type would make that chip less competitive in the market.