BLUE-THREE and YELLOW-THREE refer to a local global object called LADDER. There is no such object, but there is one called STAIRS, which has "LADDER" as one of its synonyms.
So these two rooms should probably refer to STAIRS, like RED-THREE and GREEN-THREE does.
This is fixed as part of https://github.com/the-infocom-files/starcross/pull/4 but in case that's not accepted...
BLUE-THREEandYELLOW-THREErefer to a local global object calledLADDER. There is no such object, but there is one calledSTAIRS, which has "LADDER" as one of its synonyms.So these two rooms should probably refer to
STAIRS, likeRED-THREEandGREEN-THREEdoes.