How to add multiple values for one attribute?

How to add product attribute in Opencart so that I can get specification of a product as following.

Made of material-------MaterialA,MaterialB,MaterialC
Color---------------------Red,Blue, Green

Following more I am looking to implement.
1) in search page when user applies RED as filter then the product should come in search result
2)and when user select GREEN then also product should come in search result.
I am using opencart 1.5.6.4