Hi Becky,
I would not create separate product URL if the size/color are the only variations in the product description. If you do this, you're risk creating duplicate content since there's not enough unique content for each page other than the title itself.
Create one page for the product, describe all relevant information for the user, and use filters to display the size and/or color variations.
Here's an example from Amazon and how they handle products with size/color variations:
http://www.amazon.com/Rubbermaid-Access-Storage-Tote-Large/dp/B00BEUDXIG/
use filters to display variations and always use the canonical tag to point to the main URL.
Good luck!
Eliza
