I tried to change background colour of this plugin in xfce4-panel, but it seems that value is ignored. Also Marr [1] has same issue. I have another machine with older version (orage 4.6.1 for Xfce 4.6.2) and there is no problem.

I'm using version 4.8.3

How to reproduce:
1. right-click on plugin -> Properties
2. enable 'set background colour'
3. set different colour

Expecting behaviour:
Background colour shoud ge changed according to setup above.

Thanks, Martin

[1] http://mail.xfce.org/pipermail/xfce/2012-October/031438.html