One of the nice ambiguities of Magneto is his costume. Traditionally prime colors (the art ones not physics) are for heroes and secondary for villains or “monstrous” heroes like the Hulk and Thing. There are some exceptions but most golden to Bronze Age heroes fit this pattern. Once you see this you can’t unseen it everywhere.

Magneto though is one of the few/earliest with both a primary color (red) and secondary (purple). The contrasting heroic and villainous aspects of his character.

Also red is traditionally a color of revolution and purple of monarchy, so he contains that contradiction as well. He is both the mutant revolutionary but also would be mutant king.

Finally he has a cape which are less common in marvel but still generally heroic garment, but then he has a sinister looking helmet which is more of a villain item. Often when he is more heroic he is depicted sans helmet and putting it on is when he descends into villainy (it’s telepathy blocking was actually invented by the movies).