In this case it's always better to just go along with it. Your partner will be happier, you will be happy that they are happy and overall they are likely right that changing the wall colour is a good idea. If you push back you are likely going to both end up unhappy, not to say you should always just roll over and do what your partner says, but when they ask if you are going to help, that's your opening to come up with another possible suggestion.