Tone quality is reached by emulation. You need to play duets with people better than yourself. It is also reached by learning to listen while playing - that means tons of easy tunes played softly and with feeling. You also need to play in good sounding rooms like a church hall or large auditorium. No amount of buzzing will develop your sound concept. Playing easy tunes beautifully will. You will find tons of easy tunes in a Hymnbook. The tunes all have a verse. If the theme is power and glory, beautiful tone is different than when they talk about the "meek", "weary" or "downtrodden". You need to learn to play emotion. Start simple and work up. No additional method books are needed, just an open mind, easy tunes, open ears and as often as possible a buddy to switch first and second parts with.