The most discussed and frustrated part on S24 Ultra is that display colors seems to be dull. The lack of vibrant colors is clearly visible, even when compared with my S21 Ultra. Even many people said that there S10+ display colors looks much better than S24 Ultra. 
Some have suggested few solutions that improved it a bit, but for most of us those solutions didn't work or not improved it to a level where it's noticed. 
Initially Samsung team acknowledged that they are looking into it and a software update might fix it. But now, they have changed their stance and saying that users have to use various display options available in the settings to adjust the colors to their liking. Here's the link to that reply (solution as per Samsung) - https://us.community.samsung.com/t5/Galaxy-S24/S24-colors-washed-out-and-AOD-missing-options/m-p/279...

Being a Samsung ecosystem owner (Buds 2 Pro, Watch 5, S21 Ultra), this is not acceptable to me, and I'm sure it won't be acceptable to many others. I am returning my S24 Ultra. This is the only way to let Samsung listen to this issue and resolve it in an acceptable way. We can only make them listen via our wallets.