Dreadlocks and Twists are not authorized because they fall within the guidelines of being faddish and/or due to its conspicuous nature.
Wearing of Hair Clips: "Appropriateness of a hairstyle shall also be judged by its appearance when headgear is worn. All headgear shall fit snugly and comfortably around the largest part of the head without distortion or excessive gaps. Hair shall not show from under the front of the brim of the combination hat, garrison, or command ball caps. Hairstyles which do not allow headgear to be worn in this manner, or which interfere with the proper wear of protective masks or equipment are prohibited." ~ UMO CMC