These stamps were overprinted with a violet moire pattern starting in the second half of 1915. Apparently the trip to British Honduras during World War I was considered treacherous, and the overprint was used so that the stamps could be invalidated if they fell into enemy hands.
The pattern is more obvious in person than in this scan.

The 1-cent is found in green and yellow green, with green cataloging a bit higher. Scott doesn't mention the yellow green variety.