Ah ok. I've never used Whatsapp, so didn't know they haven't updated their app to support KK. But looks like you need the actual Whatsapp+ app installed to be able to theme the stuff you are looking for. It doesn't appear to be in the Play Store, and I am not totally sure of the origins, so am hesitant to post the link here to it where I found it. If you need more info, just PM me.
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