TreeHouse do nice ones, they do rugby type shirts, polo shirts. long sleeve t-shirts, sweatshirts -lots of differnt types to choose from.
They do lots of different colours and hat covers to match. You can get some lovely designs of tops from them too like quartered, plain, stars, stripes, spots etc. Something for everyone whether you're into jazzy stuff or something more sensible!!
Heres the site:
http://www.treehouseonline.co.uk/category/2
Or if you don't want to spend a lot of money just wear a normal top - long sleeved top, sweatshirt, t-shirt or whatever is comfy for you, a hat cover, boots and light coloured jods is fine. I suppose you could wear a plain coloured top like navy or black to match a plain hat cover and that would look quite smart.
I don't think you have to be colour co-ordinated just somepeople like to and it can look quite nice I think the main thing is that the clothes you wear are suitable and safe and you wear a riding hat, body protector and medical card.
I don't normally match my numnah/saddlcloth, I just usually use a plain black cotton type numnah but matching one would look nice (you can get them fromthe TreeHouse place link above)
Hope this helps
Hannah x