The planet has earth-like atmospheric pressure and size, it's in the habitable zone, and has 45% land and 55% water (that absorbed a lot of CO2), with an atmosphere of almost 98% nitrogen and not so much oxygen. It doesn't have any kind of life, it's just a desert.
It's not a one-biome planet, it will have other biomes (maybe rocky land or something).
So what should happen (like having something in the atmosphere or sea) to have more colorful deserts? Mostly I prefer gray but anything can do!
The planet will be for human colonization.