Welcome back, it has been quiet here recently.
Well, I would say my personal preference would be for a little/touch more colour and contrast just to make them stand out a little more.
I would probably a) want to use a slightly faster shutter speed to capture the horses and make them less blurry/sharper (but still get a sense of movement where needed, this is admittedly a tricky balancing act)
b) a slightly higher aperture, say f4 to make more of the horse/rider sharp.
Obviously when you are struggling for light indoors these are hard to accommodate, but one thing I've learnt doing events is not to be afraid of higher ISOs. Better to get a sharper shot at a high ISO that you can use noise reduction on, than to get something blurry that nobody wants.
The other thing I would want for a sporting event is a fast-focussing lens. Is the 50mm the fastest to focus out of all the lenses you have?
My Canon 50mm f1.8 is quite slow to focus (it doesn't have the Canon Ultra Sonic Motor system), but my Sigma 18-50mm f2.8 EX is much faster.
I don't know what focussing mode you were using, but it might be worth checking the different modes out, eg AF-C (constant) to make sure the camera is always following the action.
Just my thoughts.
