How to make a discount on specific products quantity that have specific fields I'm a bit lost with a workcase.

I'd like to apply a discount to a few line items depending on their quantity and if the product if the line items have some specific fields.

An example will be a bit clearer:
If the user orders at least 10 differents product that share the same field value (let's say 5 different tshirt with the same color), the 10 corresponding line items in the order get a 5% discount.

I'm not familiar with rules.
I tried to make some loop on line items but i'm really in the dark here.

Some advices?
Thanks!
Hopefully you're using taxonomy fields for your color on your shirts. If you are, then your solution is easy because Commerce Taxonomy Conditions will do the job. You can have it set to a quantity of a particular taxonomy field being present in an order and have it apply some discount.