Darkest shade of red appears lost in the middle shade (contrast too low). The twig colour also kinda fails to stand out from the red or the grey background.
Sticking to shading on the apple skin only, and nowhere else? That's okay as a choice, but it looks inconsistent when the skin has 4 (though effectively 3...) shades and the rest just 1.
You could put that pink to use to AA between the skin and flesh (Like in Atnas's).
At least it looks like an apple already. Atnas, your apple looks like a plum or a cherry!