While in the TE select objects tab there is a list of available shapes select the plane or shape you want to edit then hit save texture you'll find the the skin in C:/Program Files/HTC/aheditor/terrains/(your maps name here)/savedtex to edit the skin you'll need to change it from 256 color to 16 million then use whatever painting program you have, if you lack software there is lots of great freeware, anyway after you've edited your skin change it to 256 color then place it in your texsrc file you will have to create this folder then return to TE place your plane in your map to view it, hope this helps.
