Thanks for the comments and ideas guys, that's helped me determine between using blankets or barding for my cavalry. I'm going with blankets for the troopers and barding for the officers.
Justindo, so I'm now looking to order a set of saddle blankets for my Cavalry, what colour did you use for yours?
I'm thinking brown for the bridle & reins, with a red saddle blanket. I could have several different saddle blanket colours (maybe red, green, yellow, and pale blue) and use them to distinguish different cavalry units.
Another idea is to use transverse crests for Decurions, but cut them down to a smaller fan - anyone tried that?
As Tim points out, the Romans had very advanced saddles, but no stirrups, well before the beginning of the Empire. As the picture you posted illustrates, however, once a man is seated on the saddle, you see mostly the large blanket and very little of the saddle. Because of this I have personally opted for the blanket type saddle in the Native American, Viking, and Roman sets. As you state, there are many different colors to choose from (red, orange, mustard yellow, light blue, light green, black, and brown). Really any of these colors would work and, as you state, you could use the different colors to distinguish different units or ranks. I would say that red or mustard yellow would probably the two best choices for regular auxiliary cavalry, but I would use light blue for Praetorian cavalry. Orange and green would also work for something different too, and brown would be a sobering color if you didn't want everything to be so bright. I'm not sure that black would work, as it seems an odd color for a saddle blanket, but it's possible.
Here is what I have done with my mounted troops: All my auxiliary cavalry horses are brown with brown bridles and reins and mustard yellow blankets. This provides a nice contrast with their red tunics. I have two cavalrymen with yellow tunics that I use as messengers. They also have brown horses with brown bridles and reins, but I've given them red saddle blankets for contrast and differentiation. I've put my decurions on dark grey horses with red bridles and reins and red saddle blankets. Colored dyed leather would have been more expensive, so I think this is appropriate for the decurions. I haven't mounted my centurions, although they would have ridden while on the march.
I haven't thought of cutting down the centurion crest as the books I've seen show cavalry decurions with front to back crests which are usually yellow.
