Colostygia olivata, the beech-green carpet, is a moth of the family Geometridae. It was first described by Michael Denis and Ignaz Schiffermüller in 1775 and it is found in most of the Palearctic.
The wingspan is . Freshly hatched moths have green forewings. There is a darker, brown central band narrower towards the centre of the forewings. This band is edged with a white wavy line. The hindwings are smoky grey with a pale crossline. The larva is stout, slightly tapering at each end, rugose, with conspicuous tubercles and setae. It is reddish-ochreous or brownish ochreous with an interrupted grey dorsal line. The lateral and ventral surfaces are mostly dull reddish; tubercles black. The pupa is rather stout, bright red or red-brown, the abdomen darker.
Adults are in wing from May to August in one generation.
The larvae feed on Galium species. Larvae can be found from September to May.