Is it blue, gray, or gray blue?

Whether it is blue, gray, or gray blue depends on actual shade you see, as these are three related but distinct colors, and distinction is based on undertone and lightness. Blue is primary color with clear hue like sky blue, with no grey mixing. Gray or grey, both spellings same color, is neutral achromatic color between black and white with no hue. Gray blue or blue gray is mixture of blue and gray, desaturated blue with grey undertone, like slate, steel blue, or blue-gray, appearing as muted blue that looks greyish in low light. To determine, look at color in natural daylight, if it has obvious blue hue, it is blue, if it has no hue and is between black and white, it is gray or grey, if it looks like blue but washed out and dusty, it is gray blue. In Crayola terms, there are colors like Cornflower Blue and Cadet Blue which are gray blues. In car paint, many paints called gray have blue undertone and are called blue gray. For example, hospital scrubs often are gray blue. The spelling gray vs grey does not affect color, gray blue and grey blue are same. If you describe something like eyes, many people have gray blue eyes that appear blue in bright light and gray in dim light. So answer, if color looks clearly blue, call it blue, if neutral, call it gray or grey, if muted blue with grey, call it gray blue, which is common shade for cars and clothing.