[acqq]

So it was Tandy Color Computer 3 (CoCo 3). Thanks royjacobs.

Wikipedia has one more interesting detail about CoCo 3:

http://en.wikipedia.org/wiki/TRS-80_Color_Computer#Color_Com...

"Previous versions of the CoCo ROM had been licensed from Microsoft, but by this time Microsoft was not interested in extending the code further.[citation needed] Instead, Microware provided extensions to Extended Color BASIC to support the new display modes. In order to not violate the spirit of the licensing agreement between Microsoft and Tandy, Microsoft's unmodified BASIC software was loaded in the CoCo 3's ROM. Upon startup, the ROM is copied to RAM and then patched by Microware's code."