Getting
Color On Your Envelope
by Herschell Gordon Lewis
Printing a tint
onto the face of an envelope costs almost nothing if the tint is a
screened percent of one of the colors used for the type on that envelope.
Getting the same effect, with color put into the paper by the mill can
result in a heavy premium over normal costs. If you're printing an
envelope in two colors you can have an astonishingly wide choice of under
colors, tint blocks, and color bars. Using a screened version of one of
the colors you'd use for the envelope typography anyway is a good way to
get into color testing for the envelope without spending much money for
that test.
(Taken
from Direct Marketing Strategies and Tactics)