[old_tv_nut]

Ok, I calculated the visual brightness of every color as 126, using the NTSC factors of 0.3 for red, 0.59 for green, and 0.11 for blue.

However, this means that you had to adjust the Y signal level according to hue, since if you are presenting a bluish color, as the saturation (level of chroma signal) increases, the brightness of light on the screen gets lower because the blue increase contributes 11% of its beam current increase to optical brightness, while the red takes away 30% of its electrical decrease and the green takes away 59% of its decrease. Thus, the optical brightness should be below 126. Forcing the optical brightness to be 126 means that you must be changing the Y electrical signal from its original value of 126.

So, for the B-Y case, for example, the blue value has increased greatly, being much more than 40% of the way from 126 electrical value towards max. The opposite is true for greenish colors.