Hello!
Just thought I should share something with this great community, I have learned a lot from this place, so I feel I have to give something back.
This might already be known, but I give it a try anyways.
I found that the best way to change filament from a color to another, without leaving rests of the first filament in the nozzle, which eliminating the need of priming the nozzle until the old filament rests is gone.
1. Heat up the nozzle to 100 degrees celsius.
2. When it approaches 90-95 degrees, slightly start to rotate the extruder-wheel to pull the filament out of the nozzle
3. When it gets easier and easier to pull (around 100 degrees now), loosen the tightener-mechanism on the extruder so that you can freely pull the filament with your hand.
4. Pull fast with your hand now, and everything should come in one, leaving the nozzle completely empty. (You will see that the tip of the filament is shaped as the inside of the nozzle, when you see this, success!)
5. Now the nozzle is empty, and you can insert the new filament, heat it up to ordinary temperature, prime the nozzle until you see it comes out and viola, you are ready to print! This whole procedure goes actually really fast.
(this might vary from filament-brand regarding the temperature, I am using stock filament from Ultimaker in this example)
I hope this tip can help someone. I surely have helped me a lot when changing filament!