Green’s Dictionary of Slang

Twinkie n.

[a Twinkie biscuit, which is ‘brown on the outside and white inside’]

(US campus) an Asian who identifies with Caucasians.

[US]Eble Sl. and Sociability 13: Sometimes new slang extends to new areas of meaning or to areas of meaning of recent interest to the group inventing the slang, like [...] twinkie (yellow on the outside, white on the inside) for ‘an Asian who identifies with Caucasians or has a white girlfriend or boyfriend.’.