You are in Kansas, so farm country.
Farmer's can get discounted fuel for use ONLY in farm equipment, not to be used in vehicles on public roads, road taxes, and state and federal taxes are removed.
This fuel is dyed with a color that marks it as "Farm use only".
Local inspectors will often "test" for the dye by dipping fuel tanks on all vehicles at the farm to make sure no "farm use only" fuel is being used in street vehicles.
I am thinking your truck was either used as a farm use only vehicle in the past, or some one got some cheap gas at a farm.
The dye stays around for a very very very long time.
Other reason could be, if the gauge was new, it had some residue inside.
Last edited by RonD; 02-14-2016 at 01:31 PM.