In XFCE a custom cursor theme is not applied to all windows

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http://unix.stackexchange.com – I'm using XFCE on Debian Wheezy and have a cursor theme installed where all cursor images are of white color. However, the cursors from this custom theme are seen only in some windows, for example in Iceweasel. When the cursor is over other windows, such as Thunar, or over desktop background or over dialog boxes, the cursor changes its shape back to the default XFCE black theme. How to prevent such changing of the cursor shape? Maybe one needs to replace the default cursor images? In which directory they are stored? In '/usr/share/icons' I didn't find the default cursors and in the home direct (HowTos)