I tried with exactly the same OS (Win7 x64) and it works fine in the real one but not in the virtual.
Instead of using XP detection I made an ini setting "AlternateSendMethod" so users can switch modes to make PasteColor work. In my tests PasteColor works fine on Win7 too with MS Paint and MS-like color pickers but fails on others. Using the alternative send method fixes that.
So I strongly hope this malfunction is only present when running in Virtualbox
