This is just speculation, but here is my take on these games.
There could be a greater advantage gained by counting each of the coloured decks separately, but it would be very difficult to do and custom playing and betting strategies would be required to take advantage of the information.
The two hardest aspects in my opinion would be taking note of the cards both before and after they come out of the shoe, there would be no counting in pairs, and you would have to be very quick to see the back of one card in the shoe, watch it as it comes out onto the table, and get your eyes back quick enough to see the back of the next card. I can see this being very very hard if there is even a moderately fast dealer if you are trying to keep track of two counts in your head also. The second problem is that even if you can keep the two running counts, what do you do with them? Use an average? That would only be approximate because of the neutral value cards in the deck. It is conceivable that once you are nearing the cut card there would be a heavy bias towards one coloured card, and if you were ignoring the neutral cards that have been dealt you would have no way to know this, resulting in skewed counts when big bets could be at stake.
Some other matters... you will know a maximum of one card coming to your hand next (knowing the colour of it that is) if you are playing first base, but you wont know the second card or the dealers card, so how can you choose how much to bet based on this? If you take an average of the counts to make your bets, then it would be just like regular counting. I can see bets not gaining very much advantage from having two decks. Where I think some advantage could be gained is in playing decisions. You will know the colour of the next card coming out and thus you can have a better idea of when to hit or stand, but this advantage is reduced a little by the fact that if you have one positive and one negative count, and you either hit or stand based on the colour of the next card, the following card that the dealer than takes could be the opposite colour, meaning that your decision may not have been the best in the situation.
Overall, I think that computer-perfect play would yield a great advantage from this situation compared to one-coloured shoes, but I think it will be difficult to create a system that is practical and yields a worthwhile increase in edge. Of course, this is all speculation and has no math to back it up, so take it with a grain of salt. I would be interested in hearing techniques people propose to tackle this problem though, as I think it is a rather interesting situation, and I would like to do some more thinking about it, although the game are not available here.
If only there were hole cards in europe, this game would be really great in terms of playing decisions.
Hope this was somewhat useful and not too rambly.
Good luck with finding more info.