If you decide you have a specific way you'd like your variations sorted (the order in which they're displayed on eBay) you can use the Sort Variation Names page! This is a page specifically for eBay, and is not available on other marketplaces!
First, you'll go in to edit the listing you want to change:
Once you're in the Edit Listings page, you'll click on the Action dropdown to the right, and select Sort Variation Names:
You'll see your variations here, if you have multiple variation names (Color and Size) you'll see both in separate groups and can sort them individually. Just grab and move them in the order you'd like, and then Save Changes:
That's all there is to it!
If you have any questions involving sorting variations, please reach out to support!