Again, the sense is that these attacks are primarily humorous, getting people to laugh at the scribes and Pharisees. So Jesus uses uncommon words with double meanings, here the meanings of
the "blind" and "gold." The "blind" are those lacking common sense, something Jesus accuses his opponents of using the analogy of "salt" in the Sermon on the Mount. "Gold" means "golden word," but the joke is that those who are blind can see the color gold.
I find myself wondering if swearing on the "gold of the temple" somehow implied giving gifts to the temple. My sense is generally that oaths were sealed by the giving of such gives, which the Pharisees supported.
In Matthew 5:34, Jesus makes his opinion of oath-taking clear, basically telling people at the Sermon not to do it. He has also used the term "blind guides" before as well in Matthew 15:1, describing his opponents as the blind leading the blind.