Play/pause, rewind, fast forward and stop are not visible in the skins named as dark variations with the new flat player, to fix it localize these lines and replace them with the posted values. If they are not present just follow the numerical order and insert them:
<!-- 86--> <element id="Player.Control.Default" fg="225,225,225"/>
<!-- 88--> <element id="Player.Control.Highlight" fg="25,25,25" />