I disassembled the TLB file with SHOW and reassembled the pcx files with TOOLBOX, adding the color cycling.
Everything looks fine in TOOLBOX, but in the game, the black boxes and lines appear (see screenshots below).
I've looked into RA3, and technically it should be the TREES B template, but both "tree" templates produce the black holes, and the "default" template just doesn't work at all.
Is there another way to disassemble a TLB without using SHOW?
It would be really cool if I could get the color cycling to work, because it would save me from using one extra wallset just for the shore.