Dalia
Themes can either change none, some or all of the icons - Icons that aren't changed by the theme are left with the default icons.
I guess that you're another user of Partha's builds where he has changed the default theme to the abomination of grey scale.
To add the colour icons into a theme...
If you look in the Aqua Purple 2 - Legacy Icons folder, you will see a whole collection of folders: 12,18,20,22 etc
Copy these into the folder of the theme you want to change.
Also copy the gimp-imagerc.rc file into that folder.
Now you have to edit the gtkrc file that is in the theme folder you are changing.
You need to add this line to that gtkrc file and save it.
include "gimp-imagerc.rc"
And that's it done.
Kevin