The mother cat's coloration and the coloration of her kittens provide evidence that she reproduced sexually.
In cats, color patterns are often determined by genetic factors inherited from both parents. A calico mother cat (with orange, black, and white fur) typically has a combination of colors due to the presence of two X chromosomes, where one may carry the orange color gene and the other the black color gene. The kittens’ colors reflect the genetic contributions from the mother, but also from a father that is presumed to be a typical male cat (which usually has only one X chromosome).
Since one of the kittens is orange and another is black, these colors signify that they inherited different combinations of genes. In sexual reproduction, both the mother and father contribute to the genetic makeup of the offspring, leading to a variety of potential color patterns. Therefore, the appearance of the three kittens—each with distinct colorations different from the mother—suggests that the reproduction was sexual, not asexual.
Thus, the best evidence to support the choice of sexual reproduction is the complex inheritance of colors in the kittens, indicating contribution from both a male and a female parent.