I usually change the locked background color to a dark grey, and this works fine in all my patches.
However, in order to edit easily when I have a lot of white text, I need to change the unlocked background color as well, to medium grey. This setting does not seem to stick with the patch. Everytime I re-open it, the unlocked background color has gone back to white.
I have the same behaviour with 5.1.0b8 on OSX 10.4.11. You can get around it for now by [loadbang]-ing a "editing_bgcolor 0 0 1 1" message to [thispatcher]. Or you could change it globally for every patch from Options > Object Defaults.