The chameleon theory doesn't sound that bad, considering that Tonks is a Metamorphamgus. Though I don't see a chameleon as a powerful Patronus ...
Originally Posted by cmwinters
We all know that Tonks likes Lupin. It's important to show her being concerned for him; especially at a time when the Second War is in full force (post-HBP of course).
I've seen a few Remus/Tonks fics set during HBP that are one-shots, and a bit hurried. Most of them are written from Tonks's point of view. Tonks's feelings should be explored in-depth without getting excessively sentimental (and OOC).