What color and shape are most warning signs that alert drivers to hazards ahead?

Most warning signs are yellow diamonds with black symbols or text. They alert drivers to possible hazards or changing conditions ahead — such as curves, intersections, pedestrian crossings, slippery surfaces, or merging traffic — so the driver can slow down and prepare. (Temporary construction and maintenance warning signs use the same diamond shape but are orange.) The yellow-diamond coding lets drivers quickly recognize a cautionary message even before reading it. Knowing that yellow diamonds mean 'warning — be alert and prepared' is one of the most useful road-sign facts on the permit test.