Ne plus ultra strangely unremarkable (7)
I believe the answer is:
neutral
'unremarkable' is the definition.
(both can mean bland or ordinary)
'ne plus ultra strangely' is the wordplay.
'plus' says to put letters next to each other.
'strangely' indicates an anagram.
'ultra' with letters rearranged gives 'utral'.
'ne'+'utral'='NEUTRAL'
(Other definitions for neutral that I've seen before include "Taking neither side" , "Impartial; beige" , "Not siding with any party" , "Where gears are not engaged" , "not getting involved?" .)