Possible Clues:

• Could it manage to get up to being a fossil like this after a century and a half?
• Warning forever featured in book
• It's old till all is yellow
• It goes with black at Hull City
• Color of waves of grain, in song
• Color meaning 'caution' on 13-Down
• Colour of flashing beam on river
• Neither red nor green?
• Ornamental fossil resin
• Like the song's waves of grain