I am guessing Geert was possibly correct when he mentions diffraction.

In simplified terms the red/green boundary is falling across more than one pixel array on the sensor. There being twice as many green as red or blue pixel receptors it is going to be virtually impossible to get a perfect transition.  Your camera then decides what colour the image pixel should be by guessing from the data it receives from nearby receptors. 

Using a larger aperture should help with your type of camera. The trade off is you will lose some depth of field and will need to experiment to get a happy medium which gives you results you like.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html