Do you know what color Singapore passport is?

Singapore passport generally refers to Singapore visa.

A Singapore visa is the endorsement and seal of passports or other travel documents held by China or foreign citizens by the sovereign authorities to show that they are allowed to enter or leave their own country or go through border formalities. It can also be said that it is an endorsement certificate issued to them. Generally speaking, a Singapore visa is a document issued by Singapore's entry-exit administration agencies (such as the Immigration Bureau or the Ministry of Manpower and embassies abroad) to show approval to foreign citizens.