Sounds like your teacher wants you to work beyond the notes. There are many other descriptors in a score than just notes, take a look at them and apply them. Dynamics, articulation marks, tempo changes, pedaling, phrasing, breathing, tone, etc.
You can achieve tone gradation through different types of touch used on the keyboard, also the pedals add to the tonal possibilities. Often different genres of music may have different touch: articulated baroque touch, legato pedaled touch for more romantic music, flat fingers touch for impressionist music, angular touch for 20th Century works - these are only very basic descriptions.
Ask your teacher to demonstrate methods of achieving diversified tone.