Thanks, Phil - Good ideas are always welcome.
We have developed some color- and number coded stickers that can be affixed to the key - just like a number-plate to your black Model-T Ford... We'll release these shortly.
We have developed a new process for producing and deploying Yubikeys, where each key will have its public ID printed on a non-permanent sticker affixed on the sleeve. This should speed up deployment in larger volumes.
Without revealing anything at this point, even Ford introduced other colors than black after a while....
Hardware- and firmware guy @ Yubico