You can group images within an ImageSet into Swatch Sets, meaning for a specific color product you can select the same swatch image for each product image and then they will be grouped by that Swatch image.
1. Find the ImageSet you'd like to select Swatch Sets and click "Edit".
2. In the Swatch File section under each image select the correct Swatch File that represents that product and optionally add a caption which describes that color to your customers. This caption will display underneath the Swatch image.
3. Click "Save" to save your changes and update your ImageSet. Then click "Preview" to verify your changes.