Answer:
And how can I give my post title a colour background?"
The first thing I thought of trying is to go to LAYOUT > FONTS AND COLORS as described in my previous post Changing fonts and colors for New Blogger (xml).
However, Blogger for better or for worse is constantly evolving and the LAYOUT tab is no more, replaced by a DESIGN tab and apparently have moved the template designer from Blogger in Draft to standard Blogger.