Well, opinions are wildly varied on garish and gross. A good rule if you want to avoid garish is to pick one neutral color and one pop color, like parchment + red, and don't venture further than that. Contrast warm shadows with cool highlights, or cool shadows and warm highlights. Pick colors that triangulate from each other on the color wheel, or are directly across from each other. If you have a high saturated main color, pick a low saturated color that's opposing it in warmness / coolness if you aren't directly picking based from a color wheel. If you do two high saturated colors, offset them with a couple of low saturated or otherwise extreme contrasting colors, like a very light and very dark color.