||Warning signs in the U.S. of A. are flat and uninspired.
The only signs showing a bit of taste are the Falling Rock signs.
Our finds give reason to confusion. We learn from the
Manual on Uniform Traffic Control Devices
that temporary traffic control signs (like the W21-1a at hand):
are shown as yellow signs with black borders and legends..
There is also a table named Common Uses of Sign Colors where
instead of Yellow the colour Orange is ticked for this type of sign. The same document
says that The colors coral, purple, and light blue are being reserved for uses that will
be determined in the future by the Federal Highway Administration.
The only find coming anywhere near yellow is the sign from New-York where
a yellow background is shimmering through a new layer of (is it coral?) paint.
Yes, it is probably a good idea to dispense a set of decent colour swatches.