This issue, and the solution to it, is similar to the hairstyle one. If a colourist suggests a new colour that you don't want, tell them outright. It's better to be direct then it is to hate your hair. Just like before, saying something along the lines of: "I don't think that colour suits my style, so I'll stick with [insert desired hair colour here]."
Sometimes it's hard to be assertive, because the other person is just so nice. "This colour would look amazing on you," they say. Or, "This colour was made for you." You don't want to offend them, and you don't want to come off as rude. We get it, but that doesn't mean you have to unhappily accept. Instead, say something like, "thank you so much! Even though I trust you, I'm really set on dyeing my hair [insert desired hair colour here]." It's all about acknowledging their opinion, and then reasserting your own.