Originally Posted by Ascaloth
Actually, it may not necessarily be a mistake. Their school may utilize an 'rotatting colours' system, one that ensures that a student that enrolls in a particular year is given one colour for her freshman year, and then sticks with that colour all the way til senior year.
I understand what you're saying, and actually you're right. In the CG below taken from Nayuki's path at the end, when both U1 and Nayuki had advanced to the third year, you can clearly see Nayuki's ribbon is still red. Thanks for pointing it out.