The problem is still the same; Selenium only exists alongside other Grade 4 minerals and therefore is not a primary item. Whether by design, which I suspect or bad programming there is no body in the database which has only Selenium as the 'A' grade 4 mineral. If anyone finds one such body please share!
There are three separate raw material grades in use, for historical reasons, but only the "economic" scheme is used to determine the material icons.
Selenium is Grade 4 on the economic grading scheme used by material traders, but Grade 2 on the geological grading scheme used for determining which materials appear in which planetary contexts. It is Grade 3 in the engineer grading scheme used to determine the content of Engineer blueprints. (Unlike the other two schemes, the engineer grading scheme has five grades for raw materials, rather than four)
So you'll never find a planet with Selenium as a "Grade 4" - it's always a Grade 2.
If rather than collecting from geological sites you just drive around on empty bits of the planet and shoot loose rocks, this means you can actually get Selenium much faster than the other "economic G4" materials. (On the right planet, this can actually be quicker than geological sites even for geological G4 materials ... if you get lucky)