Designers kind of have a reputation. They're sort of snarky and they always have really cool glasses. And they absolutely hate anything their boorish clients suggest because GOD did THOSE PEOPLE really suggest MAUVE?!
And, anyway, yeah, I feel you, snobby designer types. Sometimes people really do make the very worst decisions. But I'm here to say that we're not ALL like that. Anyway, I'm not like that and most of the designers I know are also not like that. Yes, we have strong opinions, but...that's why you hired us, right? Still, you know your business/career best and we ought to listen.
I've been collaborating as an artist for ten years now and I've learned a bit about getting and receiving feedback over time. This collaborative history spills over into my work as a web designer, naturally. So here is my current wisdom on the subject:
It's not personal.
At least, it shouldn't be. There shouldn't be a lot of interpersonal drama around the subject of layout and color choice. If there is, then both parties probably need to step back and reassess the situation. It's easy to feel like the decision you're making could break the whole project into little pieces and waste everybody's time. If you start to feel like this fight about turquoise vs. teal might turpedo the project, step back from it for a day or two. Remember that everyone here is committed to a successful project and come back when you can collaborate instead of demand.
Doing a project without feedback is the absolute worst. I want to either hear feedback (Can this area be more highlighted? I'm not feeling the purple) or I want to hear that it knocks your socks off. Getting a non-committal "hmm" or "it's fine" is a big bummer as a designer. So even if you feel nervous about it, share what you really think. It's YOUR website/brochure/logo, and I want you to love it. If I ever develop a mind-reader, I'll let you know and you can stop giving feedback.
It's hard to give.
The fact of the matter is that it's hard to give useful feedback in any field. It take a long time to learn what's actually helpful. When I get feedback on a work-in-progress, it ranges from "Good God that's the key!" quality to "Have you ever even seen a dance before?" schmutz. And I've given bad feedback, too. So just know you probably aren't that good at it, and hopefully whoever you've hired will know to ask you the right questions. Don't worry if they come back with questions about your feedback. Sometimes you feel like the logo is just too small, but really it's the balance of the whole page that needs to be adjusted--and a good collaborator can help you figure out the difference between the two.
Don't be shy, folks! When someone you hire asks for your opinion, they want it! Give it freely (but also kindly).