[Jim E]

The speed controllers should blink yellow without a PWM input. Once a signal is identified, they will be solid yellow( or orange). If the speed controller turns red, this means it has lost it's pwm signal through a hardware fault, or through a high current fault.

Check your software. Do not switch too fast from 127 to 255. This will create a current surge in the controller, and over time, damage the controller. It is always better to pass through (127) briefly before changing direction, or gradually increase the speed from 127 to the desired speed. Do not make the $120 mistake. You will not even notice the slower transition either, since we are talking milliseconds in delay times.