istartedsomething has a post about a "citron" (i.e. yellow) Zune 4/8, but doesn't quite get the meaning of the device right:

I’ve discovered a new device color for the 4GB/8GB Zune that is not yet available for sale or mentioned anywhere in the marketing materials.

The fifth color is called “Citron” and can be simply described as citrus yellow. When this color will be available, it will bring the total choice of colors to five - pink, red, black, green and yellow. Unlike the other colors however, the squircle touch-pad is filled black instead of the same color.

Sorry, but it's not aimed at the general public. The citron Zune features 16 GB of flash RAM (not 4 or 8) and was given to everyone on the Zune team as a commemorative "ship" gift for a job well done. So while it's not impossible that we might see one on store shelves someday, I wouldn't hold my breath for this holiday season.

Same deal on the Zune 80: It's clearly on the slow track and won't be shipping in volume until December.