About the 音色, I agree with you that sometimes it's even hard for a professinal teacher to say it's good or not, but we do have common sense on music, especially for the young beginners.
Yamaha is a very popular piano in International Competitions. Generally, the competitors have 10-30 minutes to pick a piano they want to use in the competition. Most of them picked Steinway and later found out that actually every Steinway is very unique and you will need time to get use to it. But Yamaha is not like this since all the new Yamaha pianos are similar. That's the reason that makes Yamaha to get more and more popular in the competitions.
Everthing we are talking is about kids, and lots of them are just a beginners, not professional ones. They will learn how to play lots of different pianos, but not the first day when they start.
Yamaha is a very popular piano in International Competitions. Generally, the competitors have 10-30 minutes to pick a piano they want to use in the competition. Most of them picked Steinway and later found out that actually every Steinway is very unique and you will need time to get use to it. But Yamaha is not like this since all the new Yamaha pianos are similar. That's the reason that makes Yamaha to get more and more popular in the competitions.
Everthing we are talking is about kids, and lots of them are just a beginners, not professional ones. They will learn how to play lots of different pianos, but not the first day when they start.