AR 670-1
"...(2) Soldiers may wear religious headgear while in uniform if the headgear meets the following criteria.
a) It must be subdued in color...
b) It must be of a style and size that can be completely covered by standard military headgear, and it cannot interfere with the proper wear or functioning of protective clothing or equipment...
...goatees and beards are not authorized..."
and that's a fact jack
"...(2) Soldiers may wear religious headgear while in uniform if the headgear meets the following criteria.
a) It must be subdued in color...
b) It must be of a style and size that can be completely covered by standard military headgear, and it cannot interfere with the proper wear or functioning of protective clothing or equipment...
...goatees and beards are not authorized..."
and that's a fact jack