How about EGA palette next which might be kinda a step up from four colors but it's kinda also famously difficult. Well, if nothing else, it's why various DOS characters were almost always either ghostly pale or spent three weeks unprotected in the desert sun and why horror gorefest games were still insanely bright and colorful.
I started CGA which is actually included in the 16 EGA colors, but the added choices make it harder if you don't just wanna use those four and call it a day. For me though the problem is the off white... which isn't there at all and is required for me to just go on my own colors kind of autopilot. Good for what I was trying to accomplish with choosing system palettes but quite die Herausforderung!