It probably does look like a jellyfish to a regular person, but I've played through "Metroid 2" and "3" so many times in the past 10 years that I have Metroids ingrained in my brain. Also to me it looks like it has those teeth (or whatever they are) that Metroids have, and doesn't have those skinny dangly tentacles that most jellyfish have.
Incidentally, my friend says he can see Mario's face in it, too.
As I understand it, colors in pictures of nebulae are enhanced, but not randomly selected. The colors of stars and gas are based on their chemistry. Closer nebulae can be seen with faint colors, and the levels of those are greatly increased for photos in books, magazines etc. Our instruments can't see any color in further nebulae, so colors are added based on their known or hypothetical chemical compositions, giving an impression of what they might look like (again, with the contrast turned up).
Edit: I should probably post where I found the picture. -
http://apod.nasa.gov/apod/ap080825.html