I’ve noticed this on things in the past, is this harmful, is there a common cause for some of the LEDs to briefly flash a random color when power is cut?
Schematic sketch attached if that helps anyone. I'm wondering if it may be something around where I've placed the toggle switch on the + line coming from the DC source?
It is probably caused by how the power supplies drop voltage when turned off. The voltage on the Arduino and the strip will drop at different rates. It looks like the voltage on the strips is lasting longer that the voltage on the Arduino and the Arduino is kicking out a distorted signal as it powers down.
I would try a large capacitor on the Arduino supply ( the 5V pin ) to try and keep it going longer than the strip.
Interesting and that makes sense. I’ll give that a shot!