There seems to be a slight discrepancy about what is acceptable as to the color of a ladies gloves.....the American Sidesaddle Association says:
Informal Habit - Leather gloves of harmonizing color.
Formal Habit - Black leather gloves.
Victorian Etiquette dictates though that black gloves should never be worn - unless a lady is in mourning.
Corsets and Crinolines quotes:
"Black gloves are never worn for sidesaddle riding, even today unless you are in mourning."