Apparently it's one of those things that GCC permits whereas Clang does not: I had my default compiler set to Clang, and setting it back to GCC allowed the compilation to proceed without problems.
I thus backported the 0.4.9.2+git20140410-0ubuntu2 version from Utopic to Trusty and now my new color settings are preserved, but I have to ensure that the iGtk line mentioned above is removed. (It is not regenerated at next login/reboot).
Apparently it's one of those things that GCC permits whereas Clang does not: I had my default compiler set to Clang, and setting it back to GCC allowed the compilation to proceed without problems.
I thus backported the 0.4.9.2+ git20140410- 0ubuntu2 version from Utopic to Trusty and now my new color settings are preserved, but I have to ensure that the iGtk line mentioned above is removed. (It is not regenerated at next login/reboot).