I just came from the tutorial with the quicky sepia techinque and I'm very happy with the results. Is there a tutorial about colorizing BW that is as easy as the sepia technique?

I've not seen a tutorial out there, though you might try myjanee.com

Try making a new layer, set blend mode to 'color', then paint on it. For skin and hair colors there are charts in the resource section. It helps to paint way too garish, then turn down the opacity.

I personally make detailed masks before I colorize, which I feel gives me much better control and precision, but many just paint.