Some navs have the coding printed on the label

BMWM01S = Mono coding
BMWC01S = Colour coding

If you cannot see BMWM01S or BMWC01S on the label then the only way to confirm the coding is to read it with NavCoder.

Another possibility: Does your car have TV? Is the loom equipped for TV? Is the TV tuner fitted?
If you have an original loom equipped for TV, but no TV tuner fitted, then you will not see a picture until you transfer the blue plug from the TV to the nav.