The Sega Master System has 6 bit-per-pixel color, 2 bits for each of red, green and blue. You would expect values 00, 01, 10 and 11 for each color to represent 0%, 33%, 66% and 100% voltage on the corresponding pin of the Video Display Processor. However, I once connected an SMS to an oscilloscope and found voltage levels much less evenly-spaced than this - and they were quite different for different console models.

Even if the voltages had been evenly spaced, would it have been correct to use evenly-spaced values (0, 85, 170 and 255) for each of r, g and b in an emulator? I believe this would be correct, assuming that the gamma curve of a modern monitor matches that of a 1980s/90s TV - which should be the case for a monitor calibrated to sRGB?