Why is pluto not a planet?

The International Astronomical Union or (IAU) downgraded the status of Pluto planet because it's adwarf planet and because it did not meet their criteria according to the IAU. It uses to define a full-sized planet earlier. Significantly Pluto meets all the criteria but except one and that is it has not cleared its neighboring region of other objects or planets.

Pluto had Rich Color Variations. According to NASA’s New Horizons spacecraft captured that high-resolution enhanced color view of Pluto planet on the date of July 14, 2015. The image combines colours like blue and red that images were taken by Ralph/Multispectral camera.