Rather than using standard cabinetry, consider creating a sink vanity out of an old dresser. A cabinetmaker can cut a hole in the top of the dresser to fit a drop-in sink. Cover the top of the dresser with a slab of countertop in the material of your choice. Paint the dresser a punchy color to update it even further
Idea for the main level powder room. there's your pop of color on the vanity base, the framed mirror, updated light and carry the subway tiles from the kitchen into the this space for uniformity. Carry the crisp white into here too.