1: Woocommerce-> product->attribute.
2: Click on attribute(color)-> then all variations are listed (blackblue,black-silver,black-green etc).
3: Click on configure terms->as you click on that all variation will list.
4: Select any variation -> click on edit(button)-> there is an option “Display Type” from there you can select thumbnail-image/color/text which you want to display on front end.
5: Now this setting work globally for all global attributes.and swatches will show on all products.