Many Sci-Fi stories have soldiers who don't wear camouflage. Some people here might want to have a few reasons to justify why soldiers in their story don't have camouflaged armor. Here is why camouflage could be obsolete in a Sci-Fi setting:

1. Advances in drone technology.

The war in Ukraine has shown that drones have completely changed warfare. These drones are often equipped with thermal imaging cameras which camouflage doesn't really affect. Drones have become so prevalent that both the Russian and Ukrainian militaries are under 24/7 surveillance. Both countries have also started to develop drones which can operate autonomously making EW ineffective.

1. Advances in radar technology

Many countries already operate portable radar systems capable of detecting moving equipment over a dozen kilometers away. Advances in such technology might allow radar systems to detect not just tanks and artillery shells but enemy troops. Even the use of radar absorbing materials would not be fully effective against enemy radar because L-band radar is not really effected by RAM. L-band radar systems however typically require the power of an entire city to actually track enemy targets. This means the L-band radar would not be capable of guiding a missile to its target or differentiating enemy soldiers if they are less than a few kilometers apart but can provide the approximate location of enemy forces. Some countries have also begun implanting such systems onto tanks who can also send and receive information obtained by radar or drones to and from other tanks or to artillery guns. If an enemy soldier fires at a tank, the tank would be able to calculate the approximate location of the enemy soldier through the trajectory of the bullets (made easier with advances in AI) and send this information to an artillery gun to shell said location. Or it might even be capable of detecting the soldier himself.

I just wanted to provide Sci-Fi writers an excuse to give their soldiers in their story colorful uniforms while trying to be "realistic" (as realistic as you can be in Sci-Fi).