Many thanks for pointing me in the right direction. I was thinking along more simplistic lines in having optionCategoties with colour, size and image and then using dynamic drop down menu with these categories in the options input page so that when images is chosen file upload box appears instead of a text box.
I am quite comfortable with storing 2 images per colour per product line as this will be a manageable quantity. Currently 60 images.
Do you think this will work?