Apple Color 1.0 - Manual (Page 149)

Chapter 8 Video Scopes 149
Overlay
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), then 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.
Red/Green/Blue Channels
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.