Variant media and swatches
Show only the selected colour’s photos, and give colour options real swatches.
Hide other variants’ media
Turn this on in the Product information section to show only the selected variant’s media plus media shared by every variant.
Group media by position
The default in Theme settings → Media. A variant’s featured image and the media after it, up to the next variant’s featured image, belong to that variant. Media before the first variant image show for every variant.
Group media by alt text
Add tags at the end of each media’s alt text, one per option value, using the option name and value exactly as in the product. Untagged media show for every variant.
Back view #Color:Forest Green
Swatches
Swatches use the colour or image set on each option value (Products → the product → option values, or Content → Metaobjects for shared colours). A value without a swatch falls back to its name as a colour where the browser recognises it. Product card swatches swap the card image to that colour’s media.