Thanks for your help.
Guided by all your sugestions I kept looking for the source of 5251 device types being created.
I found that the Avalanche server for the RF Guns, reading barcodes in the warehouse, was configured to use device type 5251-11 (monochrome). Now has been setup to be 5292-2 (color) and all the guns work perfectly and showing the color coded fields as expected.
After removing all remaining device types 5251 in the iSeries, no new one has been created.
The problem using monochrome 5251was not restricted to the RF Guns but to any work station being assigned a QPADEV device description. All the 5251 being created for the RF Guns, and available when a standard work station signed on, were assigned and the problem spread. Some times a color device description was available and assigned and in other cases the monochrome 5251 was available and assigned. I assume that the QPADEV device descriptions are assigned by the system, sequentially.