I have found that addressable LEDs can power up in any state, while all off is the most common they can power up all on one colour. Cyan is the most common colour I have seen.
While this has not bothered me in any application I have not investigated it. If I were to investigate then I would look at the voltage rise time of the power supply. It could be too fast or too slow.
For too slow I would look at having a power supply running and then connect the power to the strip with a switch. This would be about as fast as you can get it. For two fast I would power the LED strip through a power FET and turn on the FET slowly by putting a capacitor on the gate.