Why is The Kremlin so colorful?

A little correction. This is not the Kremlin. This is the Kremlin, the seat of the Soviet and Russian governments. The image you have posted is of The Cathedral of Vassily the Blessed, or St. Basil's Cathedral. read more

The Kremlin Wall to be precise. The Wall and everything that's behind it is The Kremlin (kremlin is a type of fortress, so technically it can contain various buildings inside). read more

Grand Prince Ivan III organised the deconstruction of the Kremlin, inviting a number of skilled architects from Renaissance Italy, including Petrus Antonius Solarius, who designed the new Kremlin wall and its towers, and Marcus Ruffus who designed the new palace for the prince. read more