@TimZett I think @dankcushions posted a link (maybe in another topic) to the Shader docs in Retropie's documentation - https://retropie.org.uk/docs/Shaders-and-Smoothing/.

Oh, I forgot to mention... To play ColecoVision with blueMSX core you'll also have to get the BIOS, as pointed out in the docs: https://retropie.org.uk/docs/Colecovision/#lr-bluemsx-bios I've updated the OP with this info.