Question: what colour is plasma

Tom Nicholas answered on 14 Jun 2017:

All objects continually give off light, they glow. This light is made of “electromagnetic waves”, which vibrate back and forth with a particular frequency as they travel along. Hotter objects give off more light waves, but the waves they give off are also higher frequency.

For visible light, we see higher frequency as the light being more blue-coloured . For example a blue flame (like on a bunsen burner, or at the bottom of a candle flame) is hotter than a yellow one, and a hot piece of metal goes from red-hot to blue/white-hot as you heat it more and more.

Objects that don’t seem to be glowing are actually just glowing in colours that our eyes can’t see! For example a person’s skin doesn’t seem to glow, but if you look at it using an infra-red camera or night-vision goggles then it does! That’s because electronic cameras can see colours that our eyes can’t.

Plasmas can be almost any temperature, from about 60 degrees (as hot as a cup of tea) to billions of degrees in the hottest places in the universe, like in stars. This means they can be almost any colour! In fact, the plasmas we use for Fusion are so hot that they glow at frequencies too high for us to see, in the X-ray range! This means that in pictures of the plasmas inside tokamaks (such as the pictures on my profile), the glowing bits are actually the colder bits!