So many things will affect your visualisation, including, but not limited to:
The fixture's dimmer curve; how the 0-255 DMX signal maps to luminous intensity.
Whether the visualiser has an HDR rendering pipeline or not; without it all intensities will be haphazard.
Whether the visualiser applies any form of automatic exposure as that could counteract your dimming.
The tone mapping strategy chosen in the visualiser.
Whether the visualiser is aware of or set correctly for the colourspace of your monitor; different colour spaces apply different gamma curves.
You really need to speak with the developers of the visualiser as otherwise you stand no chance of getting it right.