Signals, Signs and Pavement Markings · Traffic Sign Colors
Warning signs
This diamond-shaped sign means WARNING. It may be yellow, yellow-green, or orange with black wording or symbols. This sign warns you about hazards or possible hazards on or near the roadway. Slow down, and use caution when you see these signs.
Learn it with your state's rules
DMV One Way teaches the whole handbook slide by slide and checks it with practice questions.