I don't think that the generic fuel name is written anywhere near the pumps in Repsol gas stations, everything is filled with the branded fuel logos and colours and such. Although, to be honest, I don't look them much when I go there xD

For now, I've been able to find more info online. On Repsol's website, they talk about Repsol Blue+ as their version of Adblue fuel, which means that Blue+ is equivalent to fuel:adblue.
Also on their website, they seem to say that Repsol's "Diesel e+" is their basic diesel, and the "Diesel e+10" their super enhanced diesel, which seems to align with the tags fuel:diesel and fuel:GTL_diesel respectively (reading from the wiki Key:fuel:* tag page)

Besides, the fuel:diesel and fuel:GTL_diesel tags do also appear in other Repsol gas station throughout the city that originally came from a 2010 import (that I should have looked before tagging my way... ups). I'll add these values and replace the old ones in my upcoming commit