Depending on the other elements in your dream (people, actions, setting, etc.), the color blue may represent one of two things, either (1) you feel peaceful, calm and tranquil in your waking life; or (2) your subconsious is trying to help you work through an actual non-peaceful or stressful situation or relationship that's in your life.
If you ask most people whether or not they dream in color, the answer is usually "no", but experts in human dreams say we all do dream in color but don't remember most dreams that way because they "fade" after waking.
I recall a dream I had years ago that was in "technicolor." The setting was the Taj Mahal, and every color was vivid and beautiful, with a bright blue sky over the palace and the long pool of water in front of the palace a brilliant blue-green. I have no idea what color that water is in actuality since I've never been to the Taj Mahal, though I've seen photographs of it all my life. I mostly just wandered around in my dream and marveled at the beauty of it all, the colors, the graceful arches of the architecture, tiles, spires, etc. Even though the Taj Mahal is a major tourist attraction, I didn't see another person there...I was allowed to enjoy it alone.
Needless to say, that dream lingered in my memory because it was so visually arresting, but I never tried to analyze what it meant to me personally. I simply enjoyed it for its beauty. So much better and restful than a nightmare!
By the way, anyone who reads this who has experience in dreams analysis is welcome to chime in with an opinion of what my Taj Mahal in Technicolor dream meant....