These tee colours seem to be close to American tradition - reference.
Blue(*) - White - Red is what we Germans know as White(*) - Yellow - Red.
(*) Champ tees, Black for others.
The second tee is "Gold", a common addition in the USA if more than three tee sets are being used.
These colours aren't set in stone (any more?). OAK uses Green - Blue - White - Red for instance, and on some courses, Blue may be shorter than Gold.
There's even a USGA article about numbers instead of colours, stating that this may be a good idea to ease the use of appropriate tees for the individual golfers' skills and shot lengths.