When we look at the other planets we see different colors because we are looking at different surfaces. When we look at VENUS, we are looking at the top of the atmosphere of Venus. Venus is permanently shrouded in clouds and when sun light falls on the clouds from above, the clouds REFLECT the light. Hence Venus appears white and BRIGHT.
When we look at MARS we are actually seeing the
rocky surface of mars. Now Mars has a thin coating of RUST (iron oxide called the mineral hematite, Fe2O3) that coats the surface. Just like rust on a piece of metal left outside on Earth. Hence when we look at Mars we see RED, the color of RUST.
When we look at the Moon we are seeing light that is reflected off the surface rocks. These rocks are of two types: the highland area is rock type called anorthosite...mainly feldspar which reflects light and is whitish. Then there is another rock called basalt that is DARK.
Go out tonight and look at the moon; can you see the two different types of
rocks based on the brightness?