On Kubuntu 9.10 with KDE 4.3.2, the same is on Fedora 21 beta:
1. Sub-pixel rendering enabled and the air theme selected: black text on gray taskbar is using grayscale rendering.
2. Sub-pixel rendering disabled and the oxygen theme selected: white text on dark taskbar is using sub-pixel rendering.
On Kubuntu 9.10 with KDE 4.3.2, the same is on Fedora 21 beta:
1. Sub-pixel rendering enabled and the air theme selected: black text on gray taskbar is using grayscale rendering.
2. Sub-pixel rendering disabled and the oxygen theme selected: white text on dark taskbar is using sub-pixel rendering.