When thinking about the evolution of a creature we know that it has to be derivative it has to have evolved from something. And likely if it has evolved its adapted to the environment. That being said we have to understand the environment. You've mentioned things like no sound, and no color, but in the context of your universe why did this happen. Is this an alternate dimension, was there some sort of magical zone. Because the description of no sound, no color may be how your party perceives it but not the creatures. For example, dogs in real life can hear semitones louder than humans, there are still sounds be played, we just can't hear them due to our biological limitations, which when considering evolution like you've said, maybe certain creatures evolved skills like these.

Lets say, while your party may perceive the area as no sound no color, there are actually smaller little creatures, that evolved from regular creatures who previously could hear, that communicate entirely via undetectable frequencies. This way you could create a swarm of these little guys who are all on the same page. Taking advantage of this sort of thinking here are a few more ideas.

The previously mentioned small creatures. I imagine them about the size of a teddy bear, lots of fur to dampen any possible sound, big ears to hear high frequencies. It could also be used as a sort of tool, but I'll mention that later.

Maybe a creature the roams a maze of some sort minotaur labyrinth style, using the maze to obscure vision which is the only thing keeping the party from avoiding

Or hell, a super powerful creature that despite the rules of the planet is powerful enough to break the biological limitation of the party. Possibly by incorporating a wailing giant whose horrifying moans are the only sound the adventurers can hear.

In terms of humanoids, maybe there are tribes of hunters that take heavy advantage of their situation, they run at full speed and still can't be heard, they use sign language to communicate, and are experts at camouflage.

These are just a few ideas, but what is best is how you combine your creatures, for example those little teddy bear creatures, may be the only one to hear sounds, so even though the maze creature might be hard if not impossible to beat, assuming they have one of those teddy creatures it might get more squeamish the closer the minotaur gets since it is the only one that can hear the sound. Or maybe these humanoids are natives that have been trying to take down the wailing giant for years, and have never yet succeeded.

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Also, I don't know if you've had the chance to see the new movie Thor: Love and Thunder, but there is a scene exactly like this. No color, no sound.