Comment 0 for bug 1244578

lightdm-session runs xrdb for .Xresources file with the -nocpp option (Line 37 and 43), which prevents the xrdb from preprocessing the .Xresources file. Many configurations like the popular solarized color theme (https://github.com/solarized/xresources/blob/master/solarized) use this and you find some complaints about in on the internet

https://bbs.archlinux.org/viewtopic.php?id=164108
https://bugs.launchpad.net/ubuntu/+source/unity/+bug/1163129
http://superuser.com/questions/655857/urxvt-uses-pink-instead-of-solarized-until-i-run-xrdb-xresources/656213

I don't see a reason for not using the preprocessor and so did the editor of Xsession (the option is not used in /etc/X11/Xsession.d/30x11-common_xresources)