Give him a call and he can talk you through it. The difference is not in the sound produced, it's in the amount of air pressure you like to use. Black for lots of pressure, white for low pressure. Once you have the right call for your bugle, then you can make any sound from that reed.
I blow very hard, so the black one works best for me. The white and green ones break over from too much pressure when I bugle, where as the black one will stand up to it. The white one is designed to still give a good loud bugle for the guy that prefers to use low pressure. The grey is in the middle. No way is right or wrong, just match up to your style.
Jason recommended that I try the grey and the Black, then order 3-4 more of the one i liked best. I think I got one of each to try. I can cow call with any of them, and can bugle with most of them, but the black is easiest for me personally.
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