Always tweed, never black. The breed is important too, for example if you are showing a small breed M+M you should wear short boots even if you are an adult
tweed jacket for M&Ms. Welsh A and Bs jod boots even if the rider is an adult. Welsh C/D jod boots or long if a child Welsh C, an adult can wear either long or short case of what looks best on pony and Welsh Cobs long boots.