Try this technique. If the cloned area still does not match, you can always add some noise.
If you are not cloning on a new and separate layer, then start.
If you look at the image, you can see that the BG goes from dark to light.
If you sample in the darker area and clone in the lighter area, your colors will not match.
Sample from the color you wish to clone.
Work up and down so your sample point remains inline with the brush.
The correct color and gradient will be cloned as you move right to left.
Work slowly and sample often.
Re-sample further away or closer to your brush accordingly.
Always in line with the sample origin.