It depends on the gases and how the photo was processed. Hydrogen gives off that classic red glow, but other elements like oxygen emit blue-green light. When those colors mix or get enhanced with special filters, you can get some wild purple and magenta shades. A lot of those amazing space photos use filtered data to highlight different elements we wouldn't normally see.
I always pictured space photos as straight-up snapshots. Learning about the filters and gas colors totally shifted how I see them. It's cool they process the images to show us the hidden details.