Apple Color 1.5 - Manual (Page 192)

The Overlay Scope
The Overlay scope presents information that’s identical to that in the Parade scope, except
that the waveforms representing the red, green, and blue channels are superimposed
directly over one another.
This can make it easier to spot the relative differences or similarities in overlapping areas
of the three color channels that are supposed to be identical, such as neutral whites,
grays, or blacks.
Another feature of this display is that when the video scopes are set to display color (by
turning off the Monochrome Scopes parameter), areas of the graticule where the red,
green, and blue waveforms precisely overlap appear white. This makes it easy to see
when you’ve eliminated color casts in the shadows and highlights by balancing all three
channels.
The Red/Green/Blue Channels Scopes
These scopes show isolated waveforms for each of the color channels. They’re useful
when you want a closer look at a single channel’s values.
192 Chapter 8 Analyzing Signals Using the Video Scopes