Finding these instructions on how to crochet with two colours was immediately trying it out ;-))
And it worked!
On the photo you can see my UFO (unfinished object) on this technique (yes, it is still unfinished, I only said that I tried it ;-))).
Links:
Tapestry crochet for right-handers
Tapestry crochet for left-handers (a service I have never seen before!)
More crochet instructions (also on tapestry crochet)