SGB format is incorrectly defined, both in Help and functionality

[HeyItsLollie]

In Tilemap Studio's Help document, SGB format is described:

SGB border: Bytes come in pairs; a tile ID and an attribute byte. The only supported attribute bits are a choice of four palettes (each with four colors) and X/Y flip.

The palette information is true for the Game Boy portion of the screen, but incorrect for the actual border. From GBDev's Pan Docs:
https://gbdev.io/pandocs/SGB_Color_Palettes.html

The SGB/SNES provides 8 palettes of 16 colors each, each color may be defined out of a selection of 32768 colors (15 bit). Palettes 0-3 are used to colorize the gamescreen, only the first four colors of each of these palettes are used. Palettes 4-6(*) are used for the SGB Border, all 16 colors of each of these palettes may be used.

* Pan Docs actually states Palettes 4-7, but BizHawk shows that Palette 7 is reserved for the Super Game Boy menu.

Color 0 is a "global" color shared among palettes 4-6 for the SGB border. This means each of the four SGB border palettes can have 15 unique colors + 1 shared color.

[HeyItsLollie]

After attempting another test today (while using Tools > Image to Tools), I've realized that Tilemap Studio itself incorrectly assumes that Super Game Boy borders only use four colors per tile. They should be treated the same as SNES tiles.

[Rangi42]

Yeah, the "SGB border" format was intended for the limited Pokémon Gen 1 and 2 borders. Just using the "SNES tiles + attributes" format for fully-general SGB borders should work.

I'll update the docs to clarify this, since there's no use in having the two formats be identical.