In 1.9.1, there is a filter inside the application /design/frontend/rwd/catalog/product/view/media.phtml, which excludes any image with a label that matches any of the color options. All other images that you upload to the custom product will be displayed.
In the custom product, go to the images tab and check your images:
You need one image to be checked as Base, Small and Thumbnail (optional) One or more additional images, which will be shown below the "Additional Views" (for one color only). Do not load all color options. One image for each color parameter to be used as a sample. Name each color name and add the suffix "-swatch" (that is, Light Green-swatch)
The RWD Magento 1.9.1 theme will replace the main image only when you click on the color of the sample. The images below "More Views" will remain the same.
You can find more information on this article.
source share