brown envelope; manila envelope
Refers to the brownish, unbleached paper envelope commonly used for official documents, invoices, or mailing. The color is implied by 茶 (brown).
I put the invoice in a brown envelope and sent it.
Please write the address on the manila envelope.
Compound of 茶 (brown) and 封筒 (envelope). The exact historical derivation is uncertain, but the term straightforwardly describes the brownish color of the envelope.