I don't get what the problem is, but whenever I want to test my new Magtorch weapon, the sprite appears in a white square, and is discolored slightly.

Is there a way to fix this?

I managed to fix it by copying an image and editing the torch over it+saving it

I don't exactly know what caused the problem though.

This is a pretty common problem for beginners. All used sprites excluding glows are required to be in the game's palette.

Tutorials on palettes; Gimp or Paint/Photoshop

I used to copy the sprite files and use them before, it worked well for me as a starter.