One data point about Apple's preference: Safari's Bookmarks menu uses a "globe" icon for pages that lack their own icon, and that monochrome globe icon does switch between light and dark when selected.

I was always searching at the wrong place.

The blue hue wasn't a problem of the style, it was a problem of the icon. Here is the solution:

for all icons

m_clientIcon.normal.addFile("plugins\\qtTsOverlay\\client.png");

add this

m_clientIcon.normal.addFile("plugins\\qtTsOverlay\\client.png", QSize(), QIcon::Selected);