Pale colour (6)
(Other definitions for pastel that I've seen before include "Crayon - gentle shade of colour" , "Artist's crayon" , "Type of crayon" , "Delicate shade; crayon" , "Pale or light colors" .)
'pale colour' is the definition.
This is the entire clue.
(Other definitions for lilac that I've seen before include "Mauve-like colour" , "Lavender colour" , "Tree - pinkish-purple colour" , "Flowering tree of the olive family" , "Plant" .)