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I don't have Max installed on this computer, but I can just explain it.
It is actually pretty straight forward.
each uzi represents a single color plane of RGB.
uzi-B spits out values from 0 to 255.
each value of uzi-B triggers uzi-G to spit out values from 0 to 255.
and in turn each value of uzi-G triggers uzi-R to spit out values from 0 to 255.
values from uzi-B and uzi-G is collected in a [pack 0 0 0] as the second and third inlet argument.
values from uzi-R triggers the [pack] as it is the first inlet argument.
in the end you get a RGB list for every possible values...
I hope this helps (I can post an annotated patch later today).
you could also put the patch in debug mode and step through to better understand the process; control loops in max are always tricky to implement and get your head around (due to the unsuitability of data-flow model)