Continuity mistake: Whale commits suicide by drowning himself in the pool. When Clayton pulls him out the color of Whale's suit changes from black to brownish, and vice versa when Clayton throws him back in. Varying degrees of wetness should not be the reason as he should be drenched too while he is lying at the poolside.
Factual error: The supposedly Great War vintage gas mask James Whale finds and later gets Clayton to wear is in fact a British style introduced in the 1930's, and the specific variation shown was not made except during WW2. In addition, during the flashbacks to WW1, various pieces of WW2 equipment crop up (e.g. helmets with spring-loaded canvas covered chin straps instead of leather chin straps, and WW2 British pattern gas mask bags).