Species within the genus Eurema (Grass Yellows) range from Asia, Africa, Australia, and Oceania, to the Americas.
The Grass Yellows are generally weak flyers, fluttering low around bushes and flowers.
At least 71 species are currently known. 
They are generally difficult to tell apart and what makes it even more difficult is that the sexes often differ slightly and there are different seasonal forms (wet and dry season forms).
The main differences between the species are:
a) the number of black spots on the underside of the forewing, combined with
b) the shape of the (apical) black markings on the upperside of the forewing and
c) the shape of the apical area markings on the underside of the forewing. 

Eurema sari (36–42 mm), sometimes also called the Chocolate Grass Yellow, is a butterfly in the family Pieridae. 
It is found in Southeast Asia.
Adults have a distinct solid brown apex on the underside of the forewing which instantly sets it apart from the other Eurema species found in Singapore. 
This species is quite common, and can be found in many locations in the nature reserves as well as in urban areas in Singapore.

This is the subspecies Eurema sari sodalis found in Singapore.

Sungei Buloh Wetland Reserve, Singapore, 25 October 2022