I love this series of Doctor Who related two color art prints by artist Timothy Doyle. There's one very obvious omission in the set and I'm not sure if there is a significance to they pairings or not. In some cases I can certainly imagine a connection between the two characters, others not so much. Perhaps it just came down to color choice and printing. Regardless some lovely work. You should check out his other stuff too.
Source: Flickr - Timothy Doyle