How to change the webmail background colour?

Dear all,

I'm quite impressed by the quality of your e-mail service and am seriously considering adopting it. Unfortunately there's a particular characteristic that has so far hindered me from shifting: the white background of the webmail interface. It is too aggressive and I can only stand it for a few minutes. I tried the alternate themes with Stylish, but these only change the colour of the top bar (both in Firefox as in Chromium).

Is there any way to change the background colour to something more eye friendly? Is it possible to create a custom theme?

Thank you and regards,

Luís

My musings on software