I think what you're seeing is a combination of "by design" and a bug--double whammy!
The way "pgsql" is currently configured for the keywords you listed is:
<!--Keyword list 0 PostgreSQL Keywords -->
<Style Name="WORD" ForeColor="black" bold="true" />
This comes from the "\ScintillaNET\Configuration\Builtin\pgsql.xml" file. As you can see the words are configured to be styled in black and hence that is probably part of your problem.
In my testing, I also noticed a bizarre behavior that I haven't had a chance to look into yet where I had to set configurationManager.Language = "pgsql"
twice to get the complete effect. The first time styled most of the tokens, but setting it the second time picked up the other keywords you listed (albeit they were still black but now also bold as described above).
You can check my sanity by trying to set the Language property twice yourself and see if you get the same behavior. I've created issue 32402 to track resolution of this. Please report any additional findings there.