When Father Mulcahey storms into the mess tent after the Cardinal's arrival and Hawkeye tells him about Sturgis' leukemia, he's wearing his priest's shirt and collar under his robe. Supposedly he went straight to post-op to talk to Sturgis and spent the night there. However, in post-op later that morning, he's only wearing a T-shirt under the robe.
The cassock the cardinal is wearing during the Sunday service appears incorrect. The one he's wearing may seem trimmed in a sort of purple, not the scarlet which would be worn by a Cardinal. But it's a very pinkish red if you correct the color setting on your TV set.