Yep. All those fantastic color pictures of the Orion nebula are just that. (Personally I think there should be a requirement to post, alongside them, true color photos.)
Why? Many times the true colour images aren't even available. How would you represent an infrared or x-ray picture properly, in your view?
False colour images aren't meant to mislead. They're meant to be more useful to understand what you're looking at. "True colour" has no meaning, really.
I'd say because without a modicum of knowledge you'd take it for granted. Compare to "images" of dinosaurs where you'll often read "this is what it should look like" vs "we know squat about the color of their skin". And for space pictures, which are 99% touted as "pictures" and not reproductive works, it's even worse.
Hell, as I'm writing this I'm tempted to double check what I know about color-correctness of any space photo, and my point was already that I'm in the second stage of not knowing - that there could be something I don't know [0]
Why aren't space photos real? For deep space photos, where we have to wait for individual photons, maybe they're false color, but many photos are taken by putting colored filters in front of the lens and then combining the exposures, so they are actually true color.
I'm not saying they're fake - I am just saying people believe what they see. So a specific or general disclaimer of "the colors might not be accurate" would be cool, if it's the case for a specific photo.
False colour images aren't meant to mislead. They're meant to be more useful to understand what you're looking at. "True colour" has no meaning, really.