ok... I've been learning to play "hey joe" (all of it, rythem, solo, and little riffs)... What i dont understand is the chromatic riff in there... It used notes in the key, yet sounds very cool... and it uses all 12 notes... this isn't exact, but it's something like this

A-3--------2-3-4-5---------4-5-6-7---
E--0-1-2-3---------3-4-5-6-----------

and then there's a turn around... but that's not what I'm intrested in...
Is there any theory I could learn about these type of riffs? (i mean even nirvana use a chromatic riff... on Anyrisum).. Or am I now entering the world of Jazz?:)
help would be much appreciated... cos i think little riffs like the above are very cool...