I have not read whether there is a definitive answer to whether Rastan supports 4 or 16-color using MCGA. There is no reason why Rastan could not support a custom graphics resolution using the adapter, as its CRT controller values can be changed.
Games that used a 320x200 graphics mode in 16 colors can look the same on TGA, EGA, MCGA or VGA. In EGA, the regular mode 0Dh is customary. In TGA or PCjr., the mode is 09h. These adapters only support 16 colors in a 200 line mode. In MCGA, the mode used will be 13h, but only the first 16 palette entries will be used. Different colors outside the 16 RGBI colors can be used by reprogramming the palette. This is not limited to "EGA emulation", some CGA games can use other than the preset palette colors by the same idea. VGA can use the EGA mode or 13h if more color is used.
IBM EGA 200-line modes are limited to 16 colors because they were designed to connect to 200-line RGB monitors that could only display 16 colors. If you wanted more color, you bought a(n expensive) 350-line monitor.
Actually, the MCGA PS/2 Models, the 25 and 30, should have very good compatibility with the PC family. They use the ISA bus, although only in 8-bit. MCGA can emulate CGA, at least the basics. They can be upgraded to VGA, I even have the card that was designed to do that for the 30. They have ROM BASIC for those pesky early programs. With an 8086 @ 8MHz, they should not be too fast. Proprietary power supply and floppy drives.
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