Dye layer navy (first half) (5)
I believe the answer is:
henna
'dye' is the definition.
(reddish-brown dye)
'layer navy first half' is the wordplay.
'layer' becomes 'hen' (hens lay eggs).
'first half' suggests halving the letters.
'navy' cut in half is 'na'.
'hen'+'na'='HENNA'
(Other definitions for henna that I've seen before include "Skin and hair dye" , "Local colour" , "natural colour?" , "hair colouring" , "A shrub, its red dye" .)