When a variation product has more than one variation, the main image does not change to reflect the choice when you choose a color. Please check this page out to see what I mean. You need to select the other variable first.
Thanks Elise for your reply, but I have already done that. The problem is when you have more than one variation, for example one for colors and one for sizes, the variation image doesn’t change before you select both variations, i.e, if size has not chosen yet and you change the color, the image doesn’t change because you need to choose a size too.
Yes, it is how WooCommerce variations work. You need to choose one term per each attribute so the system recognizes some variation and load its image. We are not able to change this behavior in our theme scope.