In general, I've always heard and gone with browns and brass for day wear, black and silver for evening. It works for me, and that coincides with HRH's attire in the above referenced photo.

Your silver fox and silver cantle sporran should be fine for any somewhat dressy to very dressy evening war. Even during the day, if you're in a black argyl with a black four-in-hand tie, it'll do fine.

It will be a little too dressy for usual day wear unless you're really dressed up. For that, almost any style brown sporran is fine. I'd go for a very plain sporran unless you can afford a nice pig skin or other pricier brown sporran.

At least, that's what I think.

And that's all I got to say about that.