color of transient-mark-mode

[Eric S Fraga]

I'm running emacs 24.4.1 on Debian Wheezy, and the background color of
transient mark is too dark, making the highlighted text hard to
read. I'd like to change the background color to a lighter color, but
I'm sure this can be done yet in my current version of emacs.

Not sure what this has to do with gnus but... You can customise any
face so you need to identify which face is responsible. Maybe "region"?