Thanks @abyeb I figured you would know this.Yes, as far as I know, this is correct. The alleles O (coding for orange) and o (coding for not orange) sit on the X-chromosome. So, for a female cat (XX), if they inherit OO they will be orange, oo they won’t be orange, and Oo they will be a tortie, torbie, or calico. Therefore, in order for a female cat to have the OO genotype, they need to inherit one O allele from each parent. This means that dad needs to be orange, and mom needs to either be a orange or a tortie.