I would suggest using alternative sites rather than the in-game designing tool. The pool of colors are just a bit small for my personal tastes and it can be harder in New Horizons since we don't have the touch screen like we did in New Leaf. A lot of the designing tips I've seen are just adding complementary colors, pretty much shading when possible. There are a few pallets with many pinks/reds that flatter each other for shading.