Set HeaderTabControl's default AccentColour to non-transparent
Set HeaderTabControl's default AccentColour to non-transparent

Avoids items disappearing if no accent colour is set.
smoogipooo/osu,johnneijzen/osu,johnneijzen/osu,ppy/osu,UselessToucan/osu,ZLima12/osu,2yangk23/osu,NeoAdonis/osu,2yangk23/osu,NeoAdonis/osu,EVAST9919/osu,smoogipoo/osu,NeoAdonis/osu,smoogipoo/osu,peppy/osu,peppy/osu,peppy/osu-new,smoogipoo/osu,peppy/osu,ZLima12/osu,UselessToucan/osu,ppy/osu,EVAST9919/osu,UselessToucan/osu,ppy/osu