Product having multiple values for attributes

If a product has multiple values for attributes size and color, how can this be modeled so I can load a demand key figure at PERPRODCUST level?

I can't have size and color as attributes of product master data type since that would mean it can only have one value.

The key figure file would be:

Product    Customer  Size      Color         Qty

A                C1           L           BLUE        10

A                C2           M          BLACK      20