Learning How To Remove Color Cast On Photos

As part of the learning process in photography is to learn how to remove color casts from photos. I searched in the internet and found these two sites (very similar) that offered a tutorial on removing color casts on photos. By the way these sites are for GIMP users and these are: 1) Grokking the GIMP  and 2) The Gimp.

So I tried to do it. And here's my result and I am not really sure if looks better or I worked on a wrong photo -- I mean there wasn't really any color cast at all.

Yellowish-greenish color cast (I think):

Removed yellowish-greenish color cast:

Did it really improve? Hmmm.. got look for something else to work on.