Tone is not something that a player who doesn't know what that is just "works on". We can work on our breathing and technique but developing a better tone comes from comparison to other players. I play duets with my students. During lessons, we play longtones together (two different tones at the same time - helps intonation too!). I often play a tune first and let the student repeat it. If I play with a full sound and add a crescendo, the chance of them doing the same is MUCH greater. When a band director says to work on tone, it is also an indication that we are playing "naively". We are not thinking about the notes before we play them and not placing each one. Some sound weak and airly, others sound simply puked out. I think that you need outside help on this. Find a duet buddy, make also sure that your teacher is playing during lessons. Emulation is the key and that HAS TO BE A ONE ON ONE EXPERIENCE! No CD of a great player can teach us to get a better tone. It can help us discover style AFTER we know what to listen for.