Answer:
What can be white and yellow at the same time?
What is found over your head but under your hat?
One am I, among six others: Largest, smallest, cold, dark and two brothers
I always run but never walk, I sometimes sing but cannot talk, No head on which a hat to place, You always look me in the face.
Other terms for this handy device include doohicky, doo-dad, and whatchyamacallit.
It is something you will never see again.