Exactly this. Only "fix" for the color problems is to use a Game Gear (consolized or handheld) and run a palette set-up program prior to starting the SG-1000 game. The SMS VDP contains an awful palette for TMS emulation modes unfortunately and it's basically ROM inside the VDP, not changeable in...
This is great! I am interested and want to buy one when that is possible. I hand-built a version without BIOS checksum defeating (so, just a wiring/connector adapter) and it works OK in some Game Gears on top of a Master Gear Converter or similar but that is pretty much it
I don't know whether it's yet "done enough" for a menu entry, but there seems to be another homebrew Neo Geo shooter under development and already available https://kakoeimon.itch.io/abyssal-infants — right now it might pretend to be "Super Sidekicks", but it would be even nicer to allow both...