Deconstruction of Costume within Horror

Within the horror genre, there are common conventions in regard to costume. The three sub-genres of horror each have shared conventions of costume, but there are some variations. 

One common theme throughout the genres is the want to portray the characters as being normal. This is so as the audience can relate to the characters and imagine themselves in the horrific scenarios they are suffering through. As a result, most costumes in all horror that are worn by the protagonists are relatively normal and generally neutral in colour and style. For example, in Insidious, a supernatural horror, the main characters all wear normal clothes.

This can also be seen in Scream, a slasher horror. 

Another aspect of costume within horror is that the antagonist often dresses differently so as to distinguish them as different and abnormal in comparison to the normal protagonists. The way antagonists are identified in the sub-genres does, however vary. 

In slasher horror, the killer will often where a mask. This mask is specific to them and they wear it every time they kill. Not only does this create a specific association with the mask and that franchise, but it adds an enigma to the plot to create a sense of intrigue and mystery as to who the killer is. 
This can be seen in the slasher horror, The Purge.