I have yet to find anything that will de-colorize
the brightly colored fibers. Not acids..alkalies..
or in this case..enzymes. The particular enzyme
used in this test had some cellulase and chitinase
in it..but after a week of soaking..the fibers were
unharmed and unchanged in appearance.
I do not see how the pigments can be any sort of
"surface coating"...they must be an integral part of
the fiber structure to be so fade resistant.
The theory that fibers pick up colors from whatever
chemical elements might be near them [copper, zinc, whatever] would not explain why some fibers [red "C"s and
the "hockey sticks"] are ALWAYS
red..or blue..never orange, yellow, green, black, etc.
On the other hand..some "species" of fibers [the flat cellulose ribbon fibers] seem to be able to pick up
any and all pigment colors..singly or mixed together.