Multi sub-attributes for manage types of colors with only one selection available

I need some help for setting up a configurable products with this features.

Let's say we are selling a cushion. We have two kind of tissues in different colors: cotton and acrylic.

Cotton is available in red and green. Acrylic id available in brown and white. So we create two attributes, cotton and acrylic and add attribute values for colors.

Now we create the configurable product cushion01 with the proper attribute set (both cotton and acrylic attribute available).

The problem is in simple products association: I can create and associate a simple but I need to define both the two attributes. And this is NOT what we want: if a user chooses "acrylic white" he cannot choose "cotton red". We only want a single attribute to be selected from one of the two tissue dropdowns.

Any ideas?

Nevermind.. I solved simply managing two different attributes and assigning attributes value to simple product. Magento does the rest switching between the two options.. It was really simple and too obvious..