How to syntax-color gutter icons like bookmark?

I've crafted my own color syntax highlighting for my most-used languages to a darker set of colors.

Now that I've made the "Gutter Background" dark I can barely see the dark-blue bookmark icon. Same problem happens for merge function with its "accept/cancel" change blocks double-arrow and X icons.

What's the PHPStorm preference for changing that type of icon that sits in the gutter? I simply can't find it.

Thanks in advance!

-Ken