It appears you're using the FatFreeCart.com service, rather than E-junkie (aka "FatFreeCart Pro"). This page documents the cart button code configuration for FatFreeCart:
Please bear in mind that we provide the FatFreeCart.com service on a strictly do-it-yourself basis with no support whatsoever (that's a major reason it's free :^), so you're expected to figure it out and troubleshoot any issues you may have with that on your own. If you decide to upgrade to the paid E-junkie cart service (aka "FatFreeCart Pro"), that does of course include support with your subscription. Since we don't normally provide support for FatFreeCart, our support team isn't very familiar with how it works, but we can try to answer your question this time.
It appears the button code for this product has been set up as two different products, one for each color, with the Item Number set as the color -- e.g.:
<input type="hidden" name="item_number" value="Blue">
With that approach, you'd normally look at which Item Number was purchased to determine the color; however, the button code for both products has an extra input tag for "item_number", and these extra tags use the same number for both products:
<input type="hidden" name="item_number" value="1"/>
Deleting the extra tag shown above for both products should restore the cart to expected behavior.