When you start buying specialty grains they are designated by color of the malt. All the barley malts start out 2 row, but the maltster will toast them to a certain lovibond (L) to designate their color. The darker the malt the darker the lovibond. I think black patent is around 160L.
Since in the above recipe the purpose of the grain is not to derive any fermentable sugars, but rather get the sweet carmel toastiness and the deep rich copper color, I found the 60L worked the best. This is not a partial mash, but rather you are simply steeping the grains in the wort to get that desired outcome. This is usually done by gently cracking the grains by rolling over them with a rolling pin and wrapping them up in a muslin bag like a giant tea bag. Then just like a tea bag they get dipped and steeped in the wort. This gives you a lot more control over flavor and color than just relying on extract. It also doesn't require the added steps of partial mashing since your fermentable sugars all come from the extract.
Specialty grains don't add much fermentable sugars to a wort being that the enzymes become compromised and the sugars become too complex to extract during the toasting process. They do add complexity, flavor, and color to the wort though. The darker the malts, the less viable sugar will be extracted even during an all grain brew.
Hope that helped.