All you need to do in your Hex Editor is replace the colour names with that of your new colour. If you go into the 'Edit' menu in your Hex Editor, you should see some sort of 'Find and Replace' tool.
Use that to change the blade texture names. Make sure your new texture has the same amount of letters as the old one though!
Also, you'll want to change the model number inside the mdl file too, otherwise if you equip the original saber at some point, your custom saber will be turned into it. Basically, the game will look at the models internal names, as opposed to the name you've given the file.
Basically, if the original file is w_lghtsbr_001.mdl, just use the Find and Replace tool to replace all instances of 'w_lghtsbr_001' to 'w_lghtsbr_099' or whatever you want.