This is an observation on something that has been a skinning challenge from the early days of MusicBee.
When an icon has transparency values and colours that match/collide with highlight colours of selected fields (and also on active tabs), these icons can loose their recognizability.
There are probably a few possible solutions for this, such as perhaps alternative icon options for 'selected', or some inverted 'masking' feature?
Or maybe a skinning option to make the (16x16?) area of the tab or the selection bar where the icon is positioned transparent?