Reassign a GeoTiff color

[Sage Lichtenwalner]

Is there an easy way to reassign a color in a GeoTiff file, i.e. replacing
"water" in a topo image with white or a color which should render as
transparent?

When I try to reassign a color using Class expressions, it then only
renders colors which I specify as Classes.  I'm sure this is something
simple, I'm just neglecting the obvious.

Thanks,

Sage
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Sage Lichtenwalner
Institute of Marine and Coastal Sciences
Rutgers, The State University of New Jersey
71 Dudley Road, New Brunswick, NJ 08901
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