Blender Git Loki

Property Search: Don't use search color for subpanel titles

This replaces the blue theme color for subpanel titles with the the same
fade as for parent panels.

The search color doesn't work well for subpanel title colors. And actually,
because there are often buttons with checkboxes in the panel headers, we
don't have to treat this indicator any differently than regular buttons.

Differential Revision: https://developer.blender.org/D8976