Acts 23:1-10 - A white-washed wall?

Acts 23:1-10, records the Apostle Paul being brought before the Sanhedrin (the local Jewish ruling council) to stand trial for testifying about Jesus. In verse 3, Paul calls the High Priest a "white-washed wall" in response to being struck due to the High Priest's command. This seems like a rather obscure thing to say in the circumstances - it hardly seems like a biting insult. So what is "white-washed wall" supposed to mean? Yes, you guessed it - it's another one of those idioms! "White-washed wall" is a very literal translation of the underlying Greek. However, the idea behind this term is that of "a dirty wall which has been made to look clean". When applied to people, as is the case in this verse, it means "a person who appears to look good but isn't". Therefore, in light of the context it would be better translated "hypocrite". Although the High Priest was attempting to uphold the Law by trying Paul, he also violated the Law by having him struck.