Like many highlighter colors (4)
I believe the answer is:
neon
'like many highlighter colors' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for neon that I've seen before include "One of the six inert gasses" , "Form of lighting" , "None (anag.)" , "Colourless noble gas" , "Noble gas used in illuminated signs" .)