Interestingly, a quick check of my records shows that ~8% of my SkyTeam flights over the past 2.5 years have been on aircraft with the SkyTeam livery (including AF A320, RO 737, ME A320, KQ E190 and KQ 737 - but somewhat surprisingly, not one from KLM). However, there is quite a lot of variation across the different years. I haven't yet done a comparison by route, but I suspect some routes are more likely to get the SkyTeam branded aircraft than others (simply because aircraft types are generally assigned to certain routes, but not every aircraft type in each airline's fleet is available in SkyTeam colours).