There are those who would pooh-pooh (or poo-poo, as it were) the concept of an art gallery in a bathroom. But on a recent Monday at a Buc-ee’s along Texas Highway 71 in Bastrop, numerous women found themselves in thrall to a glossy black horse whose portrait hung outside the women’s restroom. Undoubtedly still recovering from having watched Black Beauty at a formative age, they paused as they beelined for the stalls to lean in and read the small placard by the photo. “Black on Black,” by equine artist Samantha Carter, can be yours for $199.98—please ask for assistance.Buc-ee’s, founded in Lake Jackson by Arch “Beaver” Aplin III in 1982, has swelled to include more than fifty locations in Texas and eight other states. Its…