I don't know where exactly you are, but check your national rules. In North America as long as the jacket is darker than a certain saturation value you are all good!
I know I made the mistake of trying on a bunch of Animo stuff at a tack shop (where I got my Kep hat) and I'm now pinching my pennies to get a new tailcoat!! I have a black top hat, so I would probably get a black or dark grey one with the same cream detailing as the jacket I want too :P
I always appreciate a well dressed rider! As long as you aren't out dressing the horse and he is just as well clipped and groomed as your jacket is tailored you will definitely stand out, but in the best way!! I love fashion I just need more money :P Lol. Go for it!
They say money doesn't buy happiness -- well happiness doesn't buy horses!