My internal hard disk, the Mini's 60 gb PATA Toshiba, is seen as a removable hard drive. So instead of the normal icon, I get a yellow icon - or icons, as I've partitioned my drive into two.
So as usual, I searched high and low on the net for some clues and got some ideas including editing my IOAHCIFamily.kext but it was all in vain. I decided it was time to just deceive myself and did what was my last resort: change the icons manually.