A lot of the beautiful tone is made by psychological means i think. The piano tone is not very changeable compared to instruments like the violin or the clarinet. ...
I agree with what pianowolfi and jpaino said. When I talk about tone, I usually refer to quality of sound. Also as pointed out by leucippus, possilby not of just one not by a series of notes or a pharse.
I have to say, I think most amatuer pianist are not extremely concious of their tone quality. I have to say that I am guilty of this some of the time -- even now. The problem is not just psycological, but how you transform the concept you have into movement and eventually sound.
In my opinion, is no simple way around this but to ask someone good (a teacher!!!) to demonstrate how to make the tone and evaluate your sound, but first you need a clear idea of what a good sound is, or at least be able to identify it.
I would also like to point out a similar thing with singing instead of playing the piano. In singing there is a school called bel canto. Chopin was very found of this school btw. When I first started lessons, my teacher would make me do nothing but exercises. So I went in week after week, croaking, and really didn't understand much what she was getting at. I wasn't doing repetoir, just simple scales and holding a single note on a vowel. Sometimes she would make a funny action with her hands., or ask me to do something like say "Ladies and Gentlemen" as if I were making an announcement to a square full of people in medival times, and so other 'silly' things like that.
After a couple of months of this -- those were really frastrating months as you can imagine and I did think about quitting -- I finally understood what the point of it all was. She was trying to get me to change my singing habits, and did so by listening to and correcting the "position" of my voice. Making silly actions and telling me to imagine things was a way to get me to position the voice correctly. After a while I found that I begin to learn to identify what I good tone should sound like. The problem with singing is that the musical apparatus is inside your body. So -- she can't just say, realise this or that muscle in the throat and tighten the other one. In fact, she couldn't even really demonstrate fully what she means -- all that comes out is a good sound, and I don't know any better how she produced it.
The great thing about playing the piano is that you can actually show someone how to produce a good tone. Movement is not hidden and you can observe it. It doesn't mean that it's going to be easy, but demonstration really gets you a big step of the way there.