I think that tone is hard to talk about. It's true that the only thing you have control over when you strike a note is the velocity with which the hammer hits the string. The same velocity at impact will produce the same sound, no matter how much you worry about plucking the keys, or pulling out the sound, or kneading the keys. If the dampers are off, it's impossible to hear anything other than differences in volume (and if you are really close, differences in extraneous mechanical noises).
What makes the effect that people perceive as beautiful tone depends on how notes end (ie, how you let the dampers back down) , on voicing of chords, and on the relation between the volume of notes coming one after another. Because the things you have to do to control those factors, specifically subtle control of volume and the speed at which you come off a note, make you feel like you are caressing the key, or whatever you like to visualize, people get the feeling that such things change the tone of individual notes, even when what they do is help you control relations between notes.
For example, it seems common to think that you get a mellower more lyrical sound to the extent that you strike the key from a shallow angle rather than from the vertical. I think what is really happening is that you are getting better control of the volume of individual notes. You have to think about vectors. If you strike the key at a very shallow angle your motion is composed of a small component perpendicular to the key, which determines the velocity the hammer strikes the strong, and a large component parallel to the key, which has no effect. So a relatively large change in the force you apply at the shallow angle produces a very subtle change in the force perpendicular to the key, so by striking the key from a shallow angle you can get better subtle control of volume than you can striking the key perpendicularly. When you have subtle control of volume in a line, the line sounds beautiful and people say you have a great tone.
There are people who swear that tone is real and that you can change the quality of the onset (independent of the volume) by the manner in which you strike the key. I think that's wrong, but plenty of people think it's right.