What color is a "Cross Traffic Does Not Stop" sign?
At some intersections it is hard to tell who has the right of way. This is especially a problem for someone who has stopped at a stop sign and it looks like the other legs of the intersection also may have to stop. Two signs in the MUTCD look like they might fit this situation: R1-2a "TO ONCOMING TRAFFIC" and W4-4p "CROSS TRAFFIC DOES NOT STOP":
The W4-4p is preferred and should be Black on Yellow. It is a warning sign that alerts drivers of an unusual right of way situation. The yellow color makes it stand out; as shown in the photo below, where allowable alternative language was also used. More details on the W4-4p-"CROSS TRAFFIC DOES NOT STOP" sign and application can be found in Section 2C.50 of the MUTCD.