Last night I dreamed I was building a Dominaria sealed deck, but I started with the commons and then kept finding rares I wanted to use that weren't in my colors, so I ended up with no idea what colors I was actually in, but that was fine because #dream.
I did make up some interesting cards though: a UG legendary fish with the rules text "this cannot die," and a mechanic for building your own split cards with some kind of AND token that might actually work in silver border.