First, you must observe that this has a non-club shaped antenna making it off the sub-order of butterflies and place itself in the order of Lepidoptera – Moths. Further more, it has a resting posture in which its wings are kept downward rather than the butterflies which does not. (Observe the second picture)
White marble moth is also known as White tiger moth. The subject in the picture is a Nyctemera coleta nigrovenosa Moore ; which is the Sri Lankan sub species.
This seems almost same as Tigers in butterfly group in wing pattern at once. (There is a picture of a Tiger in the account. Try identifying differences.)
The photo was clicked at a Kandyan home garden under sunny conditions in a morning at about 8 a.m. The tree on which it feeds is a curry leaf plant (Murraya koenigii) and it rests on a Pepper (Piper nigrum) plant.