Your sound is such a precious feature of your identity that the highest compliment you can give a cellist is to say, "I love your sound". It's like saying "I love you". I tell parents to encourage their child by saying, "I love to hear you play. I love your sound." Although your instrument and the type of strings you use affect your sound, each person playing with the same cello and strings will produce their own unique sound.
Cellists talk about sound in a more clinical way by calling it tone. I think the word "tone" implies a more specific aspect of your sound. You alter your tone by adjusting the bow speed, placement and pressure. Those 3 variables can change the timbre and volume of your sound.
The way you use or don't use vibrato also has a huge influence on your sound.
To develop your sound, you must continually maintain or improve your technique. Also, use your imagination to come up with verbal descriptions of the sounds you want, using adjectives to describe the type of tone you want. Artists play around with contrasting elements, bringing out certain ones to emphasize a particular emotion, so dare to be as imaginative as possible!
