From my java code I'm returning a Set<String>. The view needs to check if the Set contains a specific string.. I can't find any docs on how Freemarker can handle this.
You can use
seq_contains. You need FreeMarker 2.3.1
This will output yes if the sequence contains "blue".
And from the comments, if you want this in an if statement
Here is the doco about it Built-ins for sequences