Hi Anna.
In my research for that console, I learned that the RF connector of the japanese SCV really change the balance of colors. You can also use the RGB outs in japan, but if i understand correctly, few did. While in france (YENO brand console), _only_ the RBG signal was transmitted on the SCART connector, and its what im using.
Some people use modified eSCV emu with different color schemes if I understand correclty (its hard with approximate japanese->english translation).
Anyhow, the current colors in MESS match what I get on my french console with RGB outs. And the new colors in SVN come from voltmeter checks that i've done myself on the truncated scart output pins.
If you can watch nicovideo
http://www.nicovideo.jp/watch/sm1325205(Japanese console with RGB outs)
more:
http://dempa.jp/rgb/heaven/g_scv.html