question about skin customization

[ironmachine]

Hi! i am editing my skin for SWBF2 using photoshop and now i have a problem. I colored the right arm of the clone trooper and consequently the left arm is also colored. I want to modify only one arm preventing the modification from also applying to the other arm. what should I do? can I do this by editing the hex tga file? Thanks in advance

p.s .: sorry for my bad English