Custom Prestashop Module Required

We need a custom module that we can plug into Prestashop, to handle product variations. It’s quite simple, there are only 2 variables – colour and size. I have photographs of each finished product. So if someone selects yellow and large, it will display that image. If they change to red (and still large) a different image will be selected. Similarly if they change size, a different photo will be selected. There are no layers or vectors, just final images. So the image must be retrieved from the database, corresponding to both size and colour. There will be several categories with products in each category. Ideally the module should plug in at product selection and exit once the product is selected.