If you are adding Product Variations (as opposed to Simple Product Options) you can add image swatches to each option that can appear in the product detail page using a couple of approaches.
This is the image field accessible when editing your product variations
The same approach that is used to add swatches to the Simple Product Options.
Each approach yields different results depending on the option display format, and product settings used.
Product Variations with Images assigned to each variation.
Simple Product Options swatches.
When adding images to the Product Variations Image field, the image is added to a single variant which can have Options/Sizes/Colours specified.
As such they are only used on single Display Format options rather than Multiple dropdowns etc.
If you have set your product page to use the Image Slider format, the images assigned here will be added to the Slider.
If you have set your product page to use the Image with thumbs, the images assigned here will be added as thumbs below the image.
If you have set up a product to use Product Variations, it is possible to still use the Simple Product Options (e.g. Manage Colours, Manage Sizes etc) area to add swatches.
These can be used when using the MULTIPLE DROPDOWNS display settings.
Colour Swatches added to the MANAGE COLOURS area, using a product with variations.
Note the MANAGE PRODUCT VARIATIONS link at the top of the screenshot which indicates the product has variations.
For example if you have a Product Variation with a color of Purple Violet, when added a Simple Product option to the MANAGE COLOURS area, you must call the colour Purple Violet, not purple violet, Purple-Violet etc.
When the Default option (or Single Dropdown) is chosen the Product Variation image swatches will show.
(A Product Variation can have colour/size/option fields all assigned with the single image.)
When Multiple Dropdown options are selected, the simple product swatches will show.
Simple product options are only available when each colour/size/option is displayed separately)
Check the Show Colour Swatches In List checkbox
in the E-COMMERCE > DISPLAY OPTIONS > Main/Category List Product Item Display Options area.