For my own desktop that uses only a gradient, I created a darker titlebar for the purpy theme.
Screenshot:
http://www.saynotogmos.org/ss/dark-titlebar-sm.png
zip:
http://www.saynotogmos.org/ss/Clearlooks-Phenix-purpy-dark.zip
IIRC the only changes made were to the xfwm4 directory so you should just be able to switch that out in the other purpy theme. But just to be sure, I zipped the whole thing.
Remember in xfce you need to change:
1. Menu > Settings > Appearance > Clearlooks-Phenix-purpy (or Clearlooks-Phenix-purpy-dark)
2. Menu > Settings > Window Manager > Clearlooks-Phenix-purpy (or Clearlooks-Phenix-purpy-dark)
And it needs to be in /usr/share/themes (not /home/user/.themes/) if you want gtk3 root apps like synaptic to be purpy too.
Enjoy!
golinux