In The Colour Out of Space , the horror is not a monster you can fight, but a color that does not exist in the known spectrum—an ontological violation.
To understand the link between the Gothic and the Eldritch, one must understand how the source of the "Uncanny" ( Unheimlich ) shifted between the 19th and 20th centuries. The Gothic presents a world where God has turned his face away, but the Devil is still watching. The Eldritch presents a universe where no one is watching, and the entities that exist are so far beyond human comprehension that they cannot even be classified as "demonic." This transition marks the movement from the horror of moral transgression to the horror of existential negation. the gothic and the eldritch pdf
The fear here is derived from the (as defined by Freud). It is something that was once familiar and domestic that has become terrifying. The vampire is a twisted version of a nobleman; the ghost is a twisted version of a mother or a lover. In the Gothic, the world is ordered by God or morality, and the horror represents a violation of that order. Critically, the horror in Gothic fiction can usually be defeated. Van Helsing can drive a stake through Dracula; the ghost can be laid to rest by revealing the truth. The universe of the Gothic is terrifying, but it is ultimately legible and moral. In The Colour Out of Space , the