The apple here has a RGB value of 251/253/252 - that's almost white, so if you try to darken this area you are going to get pretty much a shade of grey. (Although that might be ok...)
Because it's just a bit of apple (and not someone's eye for example) my approach would be to try to paint in a bit of colour, like this:-
- make a rough selection around the bit of apple (any tool - lasso, etc)
- copy and paste (puts selected area into new layer)
- roughly paint over the apple in the new layer (colour not too important yet)
- add a layer mask, then adjust/paint the mask so that only the piece of apple shows through (this is the only fiddley bit). Use a blend mode temporarily that makes the apple piece easy to identify (try 'Difference'). Once you have the layer mask set up you can easily try different options very quickly
- pick an 'apple-like' colour and paint it on the new layer
- pick slightly lighter and darker colours and paint on with a 'speckled' brush (this will give the apple some 'texture')
- you can then try any final adjustments (Hue/Sat, Contrast, Curves, etc) on the new layer to get the desired result without affecting the overall image
This sounds complicated but it's actually pretty quick when you get the hang of it. The level of difficulty just depends on how easy it is to do the layer mask.
(Quick and dirty...)
395214ED.jpg
Cheers.