In my professional opinion, I have to agree with your designer. I have used Chantilly Lace because it is a warm white, but it is still clean. It would create just enough contrast for your white tiles to stand out. I saw trust your designer. They are the expert. That is why you hired them. Correct?

Chantilly lace is one of the cleaner whites, and I'd use it in a very contemporary space if I wanted a really clean white white. If you want a more soothing calmer and less stark look, I'd go with White Dove. White dove is beautiful, soft, soothing and doesn't go yellow but will provide a nice contrast to your wall color. Going too white might make your woodwork stand out like a sore thumb and I doubt that's what you are going for.

You have Orange Peel walls. BM decorators white is a slightly grey tone white loved by designers for its ability to blend with so many colors and styles. If you use it for your ceiling do the flat; for the walls do the washable Matt finish. It is a lovely , durable finish worth the extra $$ , with a soft , velvety finish. You will not get a correct read on these colors the way you are doing this . Get some sample boards at the paint store, paint them and then hold them up to the wall. Your current wall color is interfering with your ability to see these colors correctly, you would need to prime a large area and paint a much larger sample! The painted board will allow you to move it around to different areas of the room.

SashaDog (and anyone else that wants to weigh in): See below for some pics using GAF's online visualizer. I realize it's not a perfect tool, but curious what you think about these options. As mentioned, we'll be replacing the front door and gutters, and painting the foundation and garage door a darker color (something that ties with the darkest brick color in pattern). Will likely remove the shutters too. Thanks in advance for any thoughts! The first pic is slate vs. charcoal. These are my top 2 contenders. My concerns are that the slate may appear too busy, but I do like the overall color impression (at least as appears online!). And to me, the charcoal seems too severe/stark, and doesn't really jive with the brick colors. But maybe it would work once the paint color is darker? We're aiming for a modern/mid-century modern look. And here is charcoal vs. pewter gray: Here is mission brown vs. charcoal: