How to apply themes with custom primary color (change theme color) at runtime

Say I have a theme color selector for the user to choose custom colors (hex color integer, for example) as theme color for the app, how should I do it?

This is pretty much the same question as this one, but since it's never got a proper answer and it's four years ago, I wonder if there's a way that we could do it now. Reflection methods, for example, might be able to some tricks to make it work, but I have no idea where to start with them.