image change on single attribute

Hi,
I bought this today and have a question about the product variation swatches.
Lets say I have two variations – size and colour.
I want the displayed image to change when the visitor changes the colour – because size doesn’t impact the visual difference. Yes it is a required variation, but not visually speaking.
So is it possible to change the displayed image when only the colour is changed whilst having both variations?
Thanks
Kevin