It is most likely a Scott 183, however, it could also be a Scott 178. Both come in a similar shade. The difference is in the porousness of the paper and the quality of the printing. Scott says that 178 comes on a "Yellowish Wove Paper" and the 183 comes on a "Soft Porous Paper". The difference is most easily seen by backlighting the stamp. The Soft Porous paper normally shows a mesh of small circles which can be heavy or light. The Scott 178 paper is normally harder and has more snap to the paper. The soft porous paper normally produces an impression with softer lines. There are some on so-called "intermediate paper" which makes the identification more difficult.