not 4 intro pre - novice or novice it isnt correct and u shud wear a hacking jacket at theses levels with either a tie or stock( stock shud b colured not white) at intermidiate and above black or navy jacket with a white stock is compulsery.
its not traditionally correct to wear a blue/black jacket at intro-novice but it is allowed and many do, again not sure about the tie, most wear stocks
yes i thought u were not allowed or it was improper, but i saw many riders going around in navy/black jacket even the more "top" riders who were competing youngsters.