but some teachers prefer Y, let your hand get used to it when you take exam, so, different teachers' approaches are various.

for 音色, mostly like a feeling, everyone feels different., i have experience that a great (!, who had solo concerts in Carnegie Hall) pianist, who like Peal River the most, (i rolled my eyes at that time ;-)), why pianist use Steinway? bcs, S used to sponsor/cover all the competition/exam....., but lately, Y is used , bcs, they improve their marketing. not bcs, they are good.(well, in some sense, they are good, no offensive )