Unique Records in a Column with a twist

Hi All,

I would like to place a formula in cells A2 down that does a running count of unique combinations of columns B and C.
For example, the first record is a white dog, so at that point there is 1 category of dog, next is a brown dog, so there there is now 2 categories etc.

I initially tried to adapt an array formula 1/COUNTIF($B$2:$B8,$B$2:$B8) but this wont quite do the trick.

Please see file attached.
Any ideas from anyone would be most appreciated.

Thanks

Ciaran Mc