Colourless variety of salvia (6)
I believe the answer is:
saliva
'colourless variety' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'of salvia' is the wordplay.
'of' is an anagram indicator (the answer comes from or 'of' the letters).
'salvia' is an anagram of 'SALIVA'.
Can you help me to learn more?
(Other definitions for saliva that I've seen before include "Liquid that moistens the mouth" , "body fluid" , "Clear liquid secreted into the mouth" , "Mouth secretion" , "Spit" .)