Overall the design is nice and portrays a feeling of warmth one would receive from a cup of coffee. Your color palette is an excellent choice as it represents the various colors of café mocha. However, I will say it is rather difficult to read your text near the top of glass.

Maybe add some vector steam or a stroke outline around the entire image (including white space). Test transparent textures to add some dimension.

Indeed a color gradient within each section would be interesting as all ingredients ultimately blend together with no definite separating region.