Vermillion is an alternate spelling of vermilion, a word describing a deep, brilliant shade of red. The two-l spelling is probably influenced by the word million.
The spelling of this word, describing a deep, rich shade of red often seen in enameled Chinese lacquerware, is a bit tricky. The standard spelling is with one "l" because it came to us from the French word vermeil. But because it looks and sounds so much like million, people are often tempted to spell it that way. Though dictionaries tend to accept both variants, the one-l spelling is much more common in standard edited prose.