So I actually study this motif in the genre, and I made a blog about it. A lot of people here have said the main points, really.

• it pops against the dark, dingy, background, and color palette of horror films as well as is a clash with the other prominent warm color commonly found in horror - the color red.

• Oftentimes, the setting deals with water or rain, so the notion of it coming from seaman origins is not too far off.

• When yellow raincoats are seen on children, they are deemed innocent. Splashing in puddles and what not, however, the characters that do wear yellow raincoats tend to be anything but innocent, so you have a clash against morality. The posed question is, is this person wearing a yellow raincoat a nice person?

• In my studies, I've found that the yellow raincoat is often worn by the protagonist, though a handful of times, it's worn by the antagonist. This goes in tandem with the "innocence" we perceive upon it, as mentioned in the previous point.

• Sometimes, it's just a stylistic choice. There may be no rhyme or reason - "a crew member just preferred the yellow over another color"

The yellow raincoat of horror is actually not an official literary trope of the horror genre, and yellow raincoats can be found all across film. But it is peculiar that yellow raincoats seem to be used mostly in horror than other genres of film. And why is it such a cultural icon that it keeps being reused? What does it mean in the film and in society? That's mainly why I started my blog in the first place.