The scenario described indicates that medium brown fur is favored by predators, which means that the population is likely experiencing stabilizing selection. This type of selection favors the intermediate phenotype (medium brown in this case) while selecting against the extreme phenotypes (light brown and dark brown).
As a result, the distribution curve for the mouse population would look like:
stabilizing; a tall, narrow peak in the center of the graph.
This suggests that there are relatively fewer individuals at the extremes (light and dark brown) and a higher concentration of individuals with medium brown fur, resulting in a peak at the medium phenotype on the graph.