They are popular on the Saab. 18.A. of the contract lists a "V-neck" long sleeve sweater as approved optional garments.

If you are on the Saab in MSP or DTW, you are going to need some winter footwear that is all black as well. You will see all sorts of things, but be sure whatever you get is waterproof and/or fluid proof. You cannot avoid getting de-icing fluid on your shoes on the Saab and that flight deck floor is COLD in the winter.