Color theme changer not working

For some reason I cannot change the color themes for my site from "lightest 1" to any of the other options on the list. I can do it manually, but I cannot click on "bright 2" or "dark 1". Nothing happens.
I'm I missing something?

Hi. If you still have problem, try contacting Squarespace Customer Care, they can check your site backend to troubleshoot the cause.

Hello, my squarespace site's theme bright mode color is not working, please help me on that

But dark mode color is working. please let me know reason.

I had the same issue but just fixed it. I found a broken bit of code in Settings > Advanced > Code Injection spot that I had put in. I had some styling within a <style> bracket which didn't have a closing </style> bracket. The broken code meant the colour palette settings weren't applying. Basically any broken code here or in the Custom CSS section would potentially cause this issue. Hope this helps!