perhaps you mean high saturation pixels.
highly saturated colour is that with low or no contents of white.
White is flat colour spectrum. So the flatter is the RGB(or equivalent Cyan Magenta Yellow) base.
Red is [1 0 0], or in JPEG: [255 0 0] this is 100% saturated Red.
[1 .5 .5] or [255 127 127] would be a half saturated Red
[255 255 0] is a 100% saturated Yellow. [255 255 127] is 'half clean' Yellow.
Cyan [0 1 1] Mag [1 0 1]
Another possibility is that you are just referring to the amount of Luminance (in analog TV is known as Yr) that is just the amount common to all 3 base components.
Luminance is grey scaling, which is also the output of Infrared sensors, all the colouring of IR images comes afterwards to help 'read' what is hot and what is not.
Hope it helps
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