I'll take a stab at it, and if anybody disagrees they'll fill in what I missed.
A
color scroller and a color changer are essentially the same thing. A color
fader is a different beast , but still kind of the same.
with a
scroller, you
build, or have built a "scroll" of color. first part is say R02, next R27, then r60 and so on. the scrolloer
unit fits onto the front of your instrumentand rolls the scroll back and forth to the appropriate color for the appropriate
cue. So a Color Changer or
Scroller is like a film strip that you can run back and forth in front of your
par can, but without the little
gate shutter that a
projector has you have hard transistions from color to color.
A color
fader does the exact same thing except, there are typicaly, two or three rolls of color. There are also perforations made into the transistion between colors, this allows you to essentially "mix" the colors. Not really all that different from the
CMY color mixing that is going on inside an intelligent
fixture. Instead of
dichroic filters though, your'e using "strings" of
gel. `
Here's a link to a
manual for a typical "
fader" check the end of the
manual for schematics you'll see how there are three layers of color
http://www.calstage.com/manuals/changers/morphfader.pdf
Here's a
manual for a typical color changer, notice how it shows you, at the begining, how to load A color string.
http://www.calstage.com/manuals/changers/wybforerun.pdf
BTW not endorsing either product or Calstage, these were just the first couple of links I came across that adequately illustrated my
point.
Hope that helps.