WWII Fuel Gauge MOD or not ?

I have recently come across the following instrument which at first glance appears to be a fuel gauge
Further inspection show the stores ref to be 6A/1590 MKI with a further reference number on the front of 25763/43. However the front cover shows that the white lettering has been painted over ‘SUCT’ and ‘HG’ at the bottom.
Is this some kind of hybrid gauge or a possible wartime mod or has someone tried to ‘copy’ a fuel gauge. If so why chose blue as a colour which clearly makes it different from the the correct gauge. Why go to the lengths of copying a gauge, only to paint it blue. ?
The finish and white lettering look original?