River Rock Grout Color . To make the color and shape of your manufactured stone more prominent and to create additional visual drama, choose a contrasting grout color. Apply mortar to a grout float. a coating to cover river rock shower flooring? Ceramic Tile from www.johnbridge.com Introducing seven new 2022 colored grout and sealant options inspired by the environment: Choices specific to river rock standard colors: Vincent flasch interior design inc.