How would an airspeed indicator be marked to show the best rate-of-climb speed with one engine inoperative?

The best rate-of-climb speed with one engine inoperative is indicated by a blue radial line on an airspeed indicator. This line effectively communicates the airspeed at which the aircraft can achieve the greatest altitude gain over time while operating with reduced power.

The green arc typically represents normal operating speeds for straight-and-level flight, while the red radial line indicates the maximum operating speed or the never exceed speed. The yellow line signifies caution, often used to indicate speeds that require special consideration, such as turbulence or maneuvering limits.

In this context, because the focus is on the best performance in a climb scenario with an engine inoperative, the blue radial line is the appropriate visual cue to provide pilots with the essential information they need for optimal performance during such critical flight conditions.