Is it dark gray or dark grey?

Whether you write dark gray or dark grey depends on your English dialect. In American English, the standard spelling is dark gray with an a, because American English uses gray for the color. In British English, Australian English, Canadian English, and other Commonwealth English varieties, the standard spelling is dark grey with an e, because those dialects use grey for the color. Both refer to the same shade, a deeper, more intense version of the neutral color between black and white. Both spellings are correct within their respective systems, so the choice is about consistency with your audience and style guide. If you are writing for a US audience or following American publications, use dark gray. If you are writing for a UK, Canadian, or Australian audience, use dark grey. In informal contexts many people use both interchangeably, but formal writing should maintain consistent spelling throughout, matching other regional spellings like color versus colour and center versus centre.