I have a standard 5mm RGB LED that I have connected to the digital pwm pins of my Arduino Nano and I am using a potentiometer at one of the analog inputs to change the hue of the LED. My code isn't adjusted for the LED's voltage so it uses the full range of the duty cycle. The digital pins supply 5V, so with a full duty cycle, that means at some spots on the potentiometer, I am sending a continuous 5V to some pin of the LED. However, all three channels seem to be working perfectly fine after testing it.
I previously tried sending 3.3V through all three channels of the same type of LED from the 3.3V pin without adding any resistors and blew out the red channel since it has the lowest threshold voltage (1.8) whereas the green and blue channel were okay because their threshold voltage was very close to the 3.3V. So why does my Arduino not break my LED when connected to 5V with a full duty cycle, but the 3.3V power supply breaks it?