Watch face that doesn’t change colour?

There are a number of Watch faces you can use on the Watch. I have a Series 8 and have it set to Always On, and the Face that I use does not change color at all. I use the Modular face and it does not change color when you raise your wrist, drop your wrist, etc.

Those two pictures do not look like the same face in different colors-- they look like two different faces. You can have multiple faces on the watch, and a left or right swipe choose the the next one of your choices. Try swiping to see if this is what's happening.

Change the watch face on your Apple Watch - Apple Support

Listen to what he says on the video - he is looking at what happens with Always On Display. The darker one is AOD, the borders light up to normal display when he raise his wrist.

Without knowing which Watch model you have it is not possible to advise if you can do that.

I have always on and I haven't had a single watch face change colour yet,what happens is when you drop your wrist the watch screen dims and when you raise your wrist the screen lights up to full brightness again;

Turn on and wake Apple Watch

That will not be a problem!