Images for website

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Please refer to www.framingmounts.co.uk to view images on my website.

I would ideally like to have the images change colour as clients make their colour selection. Currently their colour selection is shown in a grey box below the item image and whilst this is OK it is not ideal.

My questions are:
1. How do I draw an image of the product with a transparent layer for the colour change to happen whilst maintaining a white bevel edge on the aperture cut?
2. How do I do this for a double and triple layer mount?

Any suggestions and guidance will be greatly appreciated.