Lebanon was never a colony of a European nation. It did have the status of a mandate between 1918 and 1943. After WWI, Lebanon was made a part of the French Mandate.
We should note, however, that Lebanon was conquered and made part of an empire. This was the Ottoman Empire, which took control of Lebanon in the 1500s and remained in power over the country until the end of WWI. However, we do not typically call parts of the Ottoman Empire colonies.
Therefore, the best way to answer this question is to say that Lebanon was a mandate.