It's not that images of planets are fake, it's just that the color used to represent these celestial bodies can come in many varieties.
One of the most difficult planetary questions to answer is, is this what I would see if I was there? And the answer is no. Color variations are better used to learn about the object then trying to give us an idea of what we would see. There is more information in the color of light an object absorbs and reflects than in what color we actually observe.
As an example the planet Neptune appears blue in most of the Voyager 2 images of this planet. But if you were there, would the planet really look blue? The answer is no. At almost 3 billion miles away from the Sun, light levels are 900 times dimmer. At those light levels, all you'd see is gray. There is not enough light for the cone receptor cells in your eyes to see color.
However, from a science point of view, the color the planet's atmosphere absorbs tells you about its composition. We know that Neptune absorbs more red light than blue, which means a relatively large amount of blue light is reflected off of the planet's atmosphere. This lets atmospheric scientists know that Neptune has a relatively large amount of methane gas in its atmosphere. Methane gas absorbs the longer wavelengths (red) while reflecting the shorter ones (blue).
Color is used to bring out subtle differences that we normally cannot see with the naked eye. By "stretching" the color (i.e., giving a relatively monotone object a full range of visible colors), scientists can tease out information about the nature of the objects they observe.
Sometimes a caption will describe the process used to adjust the color
There are several reasons why you see more good pictures from amateur astronomers than from NASA assets. First, there are many more amateur astronomers, around the world, with high quality telescopes and cameras than there are NASA assets and scientists operating them. The quality of amateurs' equipment and their skill level is very high and they easily compete with professional ground-based equipment and astronomers. Amateurs also can post their results immediately and wherever they want; professionals often have some red tape to deal with before posting pictures and may want to actually analyze their results before publishing or posting them, taking extra time.
Scientists using NASA assets get to observe in wavelengths not available on Earth's surface and from directions and distances not limited by Earth's orbital position. But they also have to deal with instruments that may not have been designed with the event's object in mind (the Hubble Space Telescope is great for studying planets and galaxies but its tiny field of view is not good for showing comet tails) and with scheduling issues (How close can a camera or other instruments point near the Sun without damage? When can the data be downlinked to Earth and how long will it take?) and demands to keep the assets doing what they were originally sent up to do (Map Mars or look at a comet going by?). Data interpretation may require extra time as well, especially from instruments not designed to study the event.
After data are acquired, scientists will be spend time analyzing their results and understanding what they mean. In due time, which may be a few months to several years, scientific papers on the event will be published by journals on planetary science, astronomy, astrophysics, solar physics, or other subjects. They will add to humanity's wealth of knowledge about the event. The event won't be big news by that time, but the results will teach us more about the universe around us.