In Tolkien's The Lord of the Rings series, Sauron, and characters allied with Sauron, are frequently associated with the colors red, yellow, and black. For example, here is a description of the Haradim -- a group of men allied with Sauron -- from The Two Towers.
They the are fierce. They have black eyes, and long black hair, and gold rings in their ears; yes, lots of beautiful gold. And some have red paint on their cheeks, and red cloaks; and their flags are red, and the tips of their spears; and they have round shields, yellow and black with big spikes. Not nice; very cruel wicked Men they look. Almost as bad as Orcs, and much bigger. Sméagol thinks they have come out of the South beyond the Great River’s end.
Another example: the eye of Sauron is described in The Fellowship of the Ring as "rimmed with fire, but was itself glazed, yellow as a cat’s, watchful and intent, and the black slit of its pupil opened on a pit, a window into nothingness."
I could list more examples of this, but suffice it to say, the more you read the story, the more obvious this pattern becomes.
Is there a reason behind this?