Creating color in your violin playing begins with desire. You have to be engaged enough in your music to create the need for a particular sound. Sure, interpretation and style will point you in the right direction. But you also have to want to connect deeply with your piece and your own need to express yourself.
Singing your music is an excellent place to start. When you sing, you may be reminded of other times you have felt connected to the music or performances by other musicians that have been particularly inspiring. Notice what part of your voice you are using. Is the motivation for your sound located deeper in your vocal range or is it in your head voice?
Bow speed, weight, and vibrato together, can create an index. I begin teaching this “index” to my students in the 2nd movement of Concerto in A Minor by Antonio Vivaldi, arranged by Tivadar Nachéz. This piece, marked pianissimo, is played beautifully with subtle vibrato on each sixteenth note, with a slow and somewhat heavier bow. I encourage students to adjust all three of these aspects until they find the color they are looking for. It makes all the difference in terms of drawing in the audience and feeling as though you are speaking your truth.