This system variables has the values 0 (false) and 1 (true). In 5.4 we have changed our scheme for how a module node inherits its color.
The old inheritance scheme: pre-5.4 a module would inherit its color from a containing module.
The new inheritance scheme: in 5.4 and after a module inherits its color from the color of the module class as set in Node style defaults, which make module color inheritance consistent with non-module node color inheritance.
However, there are legacy pre-5.4 models still usable in 5.4 and, in case bringing them up in 5.4 is expected to have them use the same colors as before, we provide this system variable to control which scheme is used. If this is set to true, we use the new scheme. If this is set to false, we use the old scheme.
If we bring up a model that indicates it was last saved before 5.4, we set this variable to true and if this model is saved in 5.4, we save the value of this variable as true with the model, so we have a permanent indication that it is a legacy model.
If we bring up a model that was saved in 5.4, the last value of this variable has been saved in the model file, so this handles both cases, of models created in 5.3 or before and saved in 5.4 or created and saved in 5.4.
You can of course change this back to false to get the new inheritance scheme. But you can then change it back to true to get the old.
To make this user friendly, if your model is recognized as being created in 5.3 or earlier, but you use Node style defaults to set the color of any module type, we automatically set this variable to false so that your setting in Node style default takes over. You can always set the variable to true again to back this out.