Advice on adding a product variable with incremental pricing

We have a product table:

ProductID
Product Name
Price

A variables table (colour):

ColourID
Colour
Additional Price

And a link table:
rowID
ProductID
ColourID

The link table assigns which colour variables are available for each product.

On our product detail page, I'd like to offer a radio button select option for the colour because we'd like it set so that you can only order one colour variant at a time.

Problems with this...

If we offer a discount of 10% for 10+ purchases of an item, and someone has ordered 5 blue and 5 red, then will eCart pick up on that and still apply the discount?

How do we get the additional price value from the variables table to be applied to the final price before proceeding to our view basket page?

Appreciate the guidance, thank you.
NJ