I have had this discussion many times with pianists, and I am yet to be convinced.
I do not believe one's tone can be "harsh" or "weak" or "colourless".
It's my belief that people use these terms to describe very small differences in dynamics. Whenever my teacher says "no no, that's too harsh", I simply play a little less loudly, and when she asks for a fuller tone, I play more loudly - and she seems very satisfied when I do so.
How can one produce a certain tone by one's touch? All you do is make a hammer hit a string. The only thing you decide is how quickly that happens. All you control is the speed.
If there is a mechanical (scientific) way of explaining how it is possible to alter the way the hammer hits the string, please explain it, for I am yet to encounter someone who can actually account for their belief in "tone" or "touch".
I used to think the same thing

I have a good understanding of the mechanics of the action and there is a thing called a "Let off" which disengages the hammer from the keys about 2mm before it hits the string.
So pretty much it leaves us with fact - a hammer is a projectile and the only thing you can control is its speed at the let off point. The greater the speed, the louder the sound.
With how hammers are designed, to simplify, they are softer on the outside and harder on the inside. So the slow hammer only "brushes" the strings with the surface and you get mellow sound at low volume and the faster it hits, the hammer string compresses the soft skin of the felt and the harder felt underneath takes effect so you get brighter "Color" if you will.
So that's the design on the piano, timbre, and design of the hammer of how it is voiced.
The faster the hammer hits, the brighter and louder, and the slower it hits the darker and softer.
So the conclusion is that its all about velocity and there is no such thing as a "Pianist's special touch".
If pianist A accelerates the hammer to 10m/s at the let off point and so does pianist B who's technique and visual touch look very different, the sound MUST be the same!
That is false and I know it sounds irrational.
The rationality begins with wood.
The hammer shank bends on acceleration. Think of it as a whip.
So depending when in the key down stroke you accelerated the hammer, and how much would change the angle which the hammer hits the string

You can press a note 2mm down slowly, then quickly accelerate the hammer. Or you can hit the note from high above and cause the shank to flex while at its resting position.
There are many ways to produce different sounds.
Another element is the procussive sound of the action. Press the sustain pedal and smack underneath the keybed with your first. The piano will glow with sound right?
Depending on how you hit the keys, you will cause this effect obviously more noticeable with sustain pedal.
If you dont think that can be heard over your loud playing, think again. If you put a tshirt over the strings at the highest octave which are always open to ring, and play something in the center of the piano, the sound of your piano will be different. There are also strings after the bridge which are aloud to ring by themselves that make the piano sound the way that it does.
Hope this made sense.
Noam