How to enforce minimum quantity for a given sku?

[PSEVS]

 I am seeking a way to enforce minimum order quantities for an individual SKU. This is for a member's only wholesale only website.

Example: SKU: X6T, which has four color options (red,white,blue,amber). When added to the cart, each color is appended to the SKU creating four different SKU's in the cart. X6T-R, X6T-W, X6T-B, X6T-A

I need the cart to be able to understand that all four of these entries belong to the same root SKU in order to ensure that the total for these four is equal or greater than a given number, say 20. This is to ensure they meet the minimum before being able to checkout.

I have not found a way to do this with shopping cart rules.

The next facet is similar. If the total quantity for a given SKU is greater than another given number, say 100, then the price for the items with the same root SKU would drop in price.

Perhaps I'm missing something. Any help will be greatly appreciated.

Thank you

[happy_shopper]

So to understand the issue, you have 4 simple products and you want to have those connected like when one of these products is selected to the cart, the other three wil automatically be dropped into the basket as well. It isn't possible to order those products individually. Have you looked to solve it when you combine the products as a bundled product or grouped product? Why not make it one product under one SKU?