You don't have to match! Tweed is correct for those classes, especially if your horse is of heavier build. If you have a show pony or hack (lightweight TB type) you could wear a blue jacket. Different shades of tweed can suit some horses better than others, but not necessarily because they match. Showing is based on tradition, that's why a tweed is correct for some horses, and blue for others, but never black (unless you're a man in an evening performance). Seeing a black jacket on a black horse makes me think of funerals!
If you need to make a choice when buying a jacket Id always go for tweed over the blue or black, you can wear tweed almost anywhere especially at the lower levels.
Yes, black jackets are mainly for SJ, and sometimes dressage.
Green or brown tweeds usually look most professional, why don't you look at some swatches and see what goes best, or I'm sure your brown one will be fine.