Colour-study of an apple

This art blog has been mercifully free of still lives, but this time I came pretty close. The assignment had to do with colour constancy and what we expect to see for a colour, and what colour is really there. I rolled up a paper into a small tube, and took it for a help while painting an apple.
Again, oil colours were used as a medium, with the help of some odourless paint cleaner and thinner-thingumajing. I worked on my favourite the F3 canvas board, and used a red apple on white-ish fabric for a subject.
The thing I found most tricky were the spots of highlight - they changed depending on light-source, of course, and looks very strong in the picture.

To my defence I'd like to say that I have since the photo was taken, gone over them a bit with a brush, so that they are now a lot less stark white and look much better. The real apple was moved from where I painted it, to where I took the photo, hence the differences in light and perspective and all. All in all it was a good excercise. It was particularily interesting to try and incorporate the shine caused by the bright cloth underneath, to work with uneven shadows, and to figure out how much blue versus yellow was needed for the not entirely pure red areas. But I've always had it easy with the yellow-to-red part of the colour spectrum, so it wasn't very hard to do this.
I might redo this, with an orange or something, and perhaps a blue cloth or something, just to give me a bit of a challenge (blue and orange being opposites on a colour wheel).
Pity, again, that the picture made the granulated canvas board look really odd, but oh well.