PayPal & Multiple Choices

I am considering Zen Cart.

I have a client who has some products that require multple choices - ie colour plus size - and sometimes the size has a different cost.

This means that I have set the size value as the cost, but this means that the actual size is not passed on, and PayPal just shows the cost. This is sort of ok when the sizes are different costs as my client can get the size ordered from the cost. However, she has now got t-shirts where the price is the same for each size, so cannot tell which size is ordered.

Is it possible to have a product with a colour choice AND size choice AND different prices for the size where necessary?

When you pay by debit card or credit card at a department store, isn't your credit card receipt just a purchase "amount" summary and the transaction ID, and date?
And the store receipt is the detailed list of what was purchased, including UPC codes and other specific product details?

Similarly, PayPal gives an overview receipt for the payment part of the transaction.
Zen Cart gives a detailed receipt for the order and what it contains.

In the case of PayPal Express Checkout, the receipt also gives the name of each of the products as well as the names of connected attributes. Perhaps this will be sufficient for you to bridge the gap between the payment receipt and the detailed receipt. To get this, just use PayPal Express Checkout as your PayPal choice.