This is a pretty cool challenge, I must admit. Took me a minute or two to find, and it's easy to lose sight of it if you look away.
As far as lost things go, I don't lose many items, surprisingly. The only thing I've ever really lost was a light blue (slightly see-through) twenty sided die. I bought two of them in a store and lost one of the dice a few years later. Even after renovating my room (I took everything out) I still couldn't find it, which probably means it's as good as gone.