This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of blue? It's still blue! It can also mean unripe, which might sound confusing, but it comes down to the fact that in Japanese there's some overlap between blue and green. So while in English we think of the "go" traffic light and unripe bananas as "green," in Japanese they're actually called "blue."