For my kilts I use different colours of hide, most recently red , but I've used green, tan, brown, black , and a favourite is natural - which ages to a lovely golden brown in time.
I use brass or two types of silver buckles, dependant on the the client , or whatever I
feel goes well with the kilt.
Yes of course they are not always seen, but it is little things like this attention to detail that I enjoy when making a kilt, and making it special for the client.