How Are the Planets Outside of Our Solar System Discovered?

They are discovered by measuring the wobble of their parent star. Basically they observer a star and try and detect gravitational effects on it by and unseen companion.

1. Where there more planets in our solar system?

Life has existed on Earth for at least 3 billion years, but probably closer to 4. How would that be possible if all planets are spiraling into the sun over time? There is no indication that is happening, and without some kind of friction there is no way it could according to our current understanding of gravity

2. When did we know the color/appearance of all the planets in our solar system?

Vector site provides a nice summary of what we know about the planets. That will be the source for my answer.Some planets were fairly well known to the ancients, but they could only use their eyes until the birth and proliferation of the telescope (starting in the 1600s) and then modern telescopes and space probes (1900s).The planets known to the ancients were Mercury, Venus, Mars, Jupiter and Saturn. Of these, Venus and Mars could be more closely observed by the eyes (with Mars appearing red), but Jupiter and Saturn appear as brighter distant stars. However, they had a clear orbit and so they fell into the "planet" category. Even the closer planets are confusing to the eye - Mercury and Venus are low in the atmosphere and/or coincide with the sun, making it hard to see any detail with the eye.Telescopes from the 1600s into the early 1900s could only tell so much. Using math and orbital mechanics, combined with telescope observations, astronomers could determine relative density, mass, orbital parameters and so on. Prominent moons could be seen too: Galileo spotted four moons with his first observation of Jupiter in 1610.The more distant planets required stronger telescopes. Uranus was not spotted until the 1780s and its rings were not spotted until 1977. Understanding of Uranus' orbital mechanics developed in the 1800s to suggest the presence of another planet, and so astronomers started looking. With the latest understanding of Uranus' strange orbit and some math, Le Verrier plotted the position of what had to be the source of the issue - and thus Neptune was found in 1846. Galileo had actually spotted Neptune in 1613 but chalked it up to a star. Neptune's first moon Triton was spotted shortly afterward, but appeared so small and faint as to be hard to calculate its properties.Pluto was not spotted until 1930. I will avoid the planet debate here, but information about Pluto was slow to come and difficult to interpret. Charon, which defines some of Pluto's behavior and being unusual as a binary system, was not found until 1978.Telescopes could also be misleading. The most famous case is Mars' canals. The presence of canals, which appeared to link oceans or oases, appeared in observations in the 1800s. Giovanni Schiaparelli produced a map of Mars in 1877 that showed them prominently. The canals and their possible origins captured the imagination of astronomers and the sci-fi community for years, although other astronomers claimed they could not see them. This craze included a book, MARS AND ITS CANALS, by Percival Lowell in 1906. When Mariner 4 observed Mars in 1965, there were no canals or oases - just a barren planet.The limits of classic telescopes started to be reached in the late 1800s. For example, the fifth known moon of Jupiter would be observed in 1892 and would be the last until photography and imaging technology (i.e., modern telescopes) became useful. Radar astronomy would provide additional data and would correct some previous observations, such as showing Venus to be very hot in the 1950s (previously Venus was thought to be swampy).Most of these earth-based observations were still relatively basic by the 1960s. Space probes had to clarify and confirm many of these observations, starting in the early 1960s with simple probes. For the gas giants, Pioneers 10 and 11 were the first visitors but were fairly basic, but the soon-to-follow Voyagers provided fantastic data that added much to what is now known - although there are still plenty of mysteries out there. Earth-based observatories still play a prominent role as well.To summarize the answer, only a few planets had color and appearance that could be estimated and guessed until relatively recently. The telescope certainly helped starting in the early 1600s, but there were still errors and limitations (the Mars canal controversy being an example). Earth-based observations have expanded our knowledge but are concerned more with physical properties (mass, density, spin rates, atmospheric parameters, etc). Space probes have been the best at determining color and appearance.

3. How true to reality are some pictures of our solar system and neighboring galaxies?

Several pictures of space objects are enhanced...true. The reason is basically because they are designed to "bring out"..certain details in different spectrums for different purposes. Whatever you look at through your camera to bring out realistic detail will depend on several things. Type of camera....magnification....light input....length of exposure.....etc. Astro photography has many levels to bring out any types of details you wish to....it all depends on how you go about it.