It is confusing at first. don't give up.
Changing to pink or red or any striking color will help a lot, and if you can't find that pink part after the reload, just leave it, work on the next part, when you'll post your skin someone might find it and drop you a line here on the forum.
Another method of finding elements is by cutting the code in two. if the element part is still showing in the same color cut the code again, till you find a half that has that line of code within it.
If there's an element that you have no idea what effect it has on the interface or a GUI part you want to changed but can't find it's element no matter what, just ask on the forum, most chances somebody else has already struggled with the same problem.
And about bitmap skins, check the SteelAndBee skin's thread
by Colagen. the first post has a link to the source files, which will give you a good start on skinning with images.
One last tip I can give you, is to get the portable version and work on your skins there. that way you can listen to your library while skinning without disruption. Just check the new skin changes in the portable, and keep the music playing on the installed app.