Subject: How can the light colour of a plasma be predicted?

I'm wondering how you could predict the colour of light a plasma emits? For
instance, I've heard that a hydrogen plasma should be purple, but isn't the sun
mostly hydrogen plasma? What factors would be involved? The elements, I'm
assuming, but what about temperature? Would a plasma glow with different colours
at different temperatures?

I hope you can help - I'm running a sci fi RPG, and I'm hoping to give my
players some answers on what colour that rocket exhaust happens to be, or what
colour that cloud of plasma around an alien ship might be.

Re: How can the light colour of a plasma be predicted?