conditional variation

I have a problem. I have multiple variations for a product and I need it to be conditional. For example, if product is size small, it would have the colors red, blue and white, and if the product is medium, it would only have colors red and blue. Right now, both variations show up, but the option white for medium also shows up if medium is selected. Is there anyway to show only red and blue for medium, but red, blue and white for small?

https://wordpress.org/plugins/wp-e-commerce/