Amanda Bynes -- My Future's In The Bag!

Amanda Bynes' post-rehab future looks very bright ... pink -- the color of choice at her prestigious fashion design school

Amanda -- carrying an oversized bag of school supplies -- appeared in the colorful lobby of the Fashion Institute of Design and Merchandising in Irvine, CA ... looking like a typical college student.

Bynes -- who lives at home with her parents -- enrolled in design classes as part of her recovery ... after she was released from rehab in December.