Dicky learnt uranium is lacking noticeable colour (7)
I believe the answer is:
neutral
'lacking noticeable colour' is the definition.
(in neutral tones)
'dicky learnt uranium' is the wordplay.
'dicky' indicates anagramming the letters (dicky can mean ill or non-functioning).
'uranium' becomes 'U' (U is the chemical symbol for uranium).
'learnt'+'u'='learntu'
'learntu' with letters rearranged gives 'NEUTRAL'.
'is' acts as a link.
(Other definitions for neutral that I've seen before include "Not taking sides in a war" , "not getting involved?" , "Not favouring one side or the other" , "A runlet? (anag)" , "Not allied to either side" .)