A lot of factors go into making a horror movie truly scary, but don't discredit how visuals and sound play into the narrative. The general precedent for horror is to use low light, shadows, and eerie or grotesque images. Look at classics such as Friday the 13th, Halloween, and Nightmare on Elm Street as examples of films you expect to be terrifying just based on visual effects alone. Some of the most creatively frightening films, however, use neon or pastel colors, sunshine, and intricate patterns to distract you from the atrocities being showcased.
Some examples of horror movies that don't look like horror movies include 2019's Midsommar, 2009's Greek masterpiece Dogtooth, and the infamous Stephen King adaptation The Shining. Though they are stunning to look at, the bone chilling stories these films tell will haunt you for years to come.