Pale purple colour (5)
(Other definitions for lilac that I've seen before include "Shrub with fragment purple or white flowers" , "Fragrant, pale purple flower" , "Pale violet hue" , "Flowering tree of the olive family" , "Purplish in colour" .)
'pale purple colour' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mauve that I've seen before include "sort of light seen in West" , "Light purple" , "Bluish purple" , "Pale purple colour" , "Shade of pale purple" .)