They're supposed to be; it was given in all their descriptions before series 3 and in their interview with Lily ages ago they said "we're playing identical twins but we're not identical" and then Lily was all "you are identical, you're identical but different" which LOL but yeah, I think so.

They're obviously not focusing on that so much these days as a) it was key to their storyline that they looked really similar in s3, same can't be said for s4 AND b)I don't think they want to draw attention to the fact that they just DON'T LOOK IDENTICAL. :)