@i dont know It's weird to put it lightly. Technically the Virtual Boy doesn't have a palette in the same way as most consoles.

The console itself has red LED lights and they are not part of the palette, all the console knows is what brightness setting to use (off, A, B, C). So basically emulators instead have to make up a palette. Some emulators you can even change the colours like with BizHawk, it shows red, blue, purple and black by default with a faked 3D effect instead of red what older emulators used (and even then the values for the red and black are different depending on what emulator you use). There are even console mods such as the VirtualTap.

As for graphics in this game, they are stored differently compared to most Virtual Boy games. If you are familiar with the ZX Spectrum because that also stores its graphics "b&w", it is similar with one layer and then a shadow mask.

how is this b&w???

I've been wondering if this should be considered a successor to the NES and GB games also called "Golf," since the US release of this really tries to drive home it being NINTENDO Golf. Then again, the Japanese release instead is all T&E, and they've made lots of golf games...