The way I would probably approach this is to have a ‘Thing’ that is ‘Product SKU’ which has a field - Product (Type Product) a SKU Attribute (Text) and attribute values (list of values - text). You may also want to have some other meta related data per attribute to describe it (such as ‘cm’ for size)
Product - Type Product
SKU Attribute - Type Text
SKU Values - Type Text - Multiple Values
Table should look something like this
Product | SKU Attributes | Values
Shirt | Colour | Red , Blue, Green, Orange
Shirt | Size | Small, Medium, Large
With these values associated to a product, you can search for SKU attributes and create a repeating group that returns the SKU Attribute per cell as a text object (so the user does not need to select it) and drop down value (populated from the values list).
The user can then select a value from the drop down of available values.
On submit, take those values and write them to what ever table you need to.
One thing I would probably also do is create a form that allows me to populate the SKU Attributes table and in the workflow I would also write each SKU Attribute instances into a list on the product so you don’t actually have to set search criteria, you can simply return the list of SKU Attributes in the repeating group.
Hope that makes sense.