Colorful desert on a lifeless planet that has water?

Question

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.

Answer 1

Geology can make pretty colored rocks without the need for life.

There are places on Earth whose toponym is a clear indication on the colorfulness of the local geology.

Example one: the Painted desert in Arizona

The Painted Desert is a United States desert of badlands in the Four Corners area,2 running from near the east end of Grand Canyon National Park and southeast into Petrified Forest National Park. It is most easily accessed from the north portion of Petrified Forest National Park. The Painted Desert is known for its brilliant and varied colors: these include the more common red rock, but also shades of lavender.

Example two: the Zhangye rainbow mountains

The Zhangye National Geopark (simplified Chinese: 张掖国家地质公园; traditional Chinese: 張掖國家地質公園; pinyin: Zhāngyè Guójiā Dìzhìgōngyuán) is located in Sunan and Linze counties within the prefecture-level city of Zhangye, in Gansu, China. It covers an area of 322 square kilometres (124 sq mi). The site became a quasi-national geopark on April 23, 2012 (provisional name: Zhangye Danxia Geopark). It was formally designated as "Zhangye National Geopark" by the Ministry of Land and Resources on June 16, 2016 after it has passed the on-site acceptance test.

Zhangye Danxia is known for the unusual colors of the rocks, which are smooth, sharp and several hundred meters tall. They are the result of deposits of sandstone and other minerals that occurred over 24 million years. The result (similar to a layer cake), was tilted by the action of the same tectonic plates responsible for creating parts of the Himalayan mountains. Wind, rain, and time then sculpted extraordinary shapes, including towers, pillars, and ravines, with varying colours, patterns, and sizes.

Answer 2

Sand is only yellow or white because it's mostly quartz obtained from breaking down granit. That's a consequence of living on a planet with a high amount of silicon-a lot of your rocks are gonna have a lot of it in them.

However, granite isn't the only rock that can be pounded into sand. Take, for example, the black sands of Punaluʻu Beach:

They're made from basalt generated by Hawaii's volcanic activity.

Or Shelter Cove Beach, created by shale erosion:

You can get even crazier colors if you go with more exotic compositions. For example, purple beaches, like what is occasionally seen on Pfeiffer Beach, are a consequence of, you guessed it, purple minerals such as garnet or rose quartz.

All you need to make sand is rocks and time, and to make pretty sand, you just need pretty rocks and time(Or a crusher).