Could this be a white form of the frequently green species Traminda viridaria , The lead photo in the Agrican Moths site is off white http://www.africanmoths.com/pages/GEOMETRIDAE/STERRHINAE/traminda%20vividaria.html There again perhaps not - see the variations within each species in BOLD systems (
http://www.boldsystems.org/index.php/Taxbrowser_Taxonpage?taxon=Traminda&searchTax= ) - no spots, little solid spots, big ringed eyes all mixed up along with the colour variations through white, browns and greens within many of the species documented.