Colourless friend has energy (4)
I believe the answer is:
pale
'colourless' is the definition.
(similar in meaning)
'friend has energy' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'has' is a charade indicator (letters next to each other).
'energy' becomes 'e' (physics symbol as in E=mc2).
'pal'+'e'='PALE'
(Other definitions for pale that I've seen before include "White" , "Upright member" , "Stake, lacking colour" , "Wan; boundary" , "A bit of fencing" .)