I'm not sure why, exactly, but when I tried to sync background color to accent color, it didn't work for me. Oh, wait, I have syncing issues with the laptop. Yep, I'm on a metered connection, so it's not syncing. I'll have to wait until I get to Wi-Fi to do it.
Seriously, though, my desktop background color isn't what I want for my accent color at all. Probably because I prefer a clean, black desktop background which means stuff would not show up with the black background on my phone with a black accent color. Ha! That would be sad... I suppose I better disable theme syncing for my phone, so I can keep it separate. Wouldn't want the same photo background either. I like a photo on the phone, but not on the desktop. I wonder, though, will it sync a photo for a background? I can see where that would be cool if you had laptop, tablet, phone, desktop, TV, etc., and had the same lockscreen photo on all, and the same photo in the background on the start screen, etc.
Someone test it with the photos and let me know if that works, since I won't be at a non-metered connection for possibly 3 days or more. Yeah, I live way out in nowhere, living just on the metered 4G for internet.