First and foremost I'd like to give a giant shout out to BPKelsy who's tutorial lighting a giant elephant changed my life ;) and is the basis for this one. Even though this tutorial is aimed at beginners and doesn't go into anything very technical, I'm going to jump right into the colour and lighting part. The elements are already positioned and the swan is (painstakingly!) masked. The original swan image is pure white. He needs colour, light and shadow to match the sunset:
The first step is to duplicate the original "swan white" layer. Select Layer/Duplicate Layer and call the new layer "swan light orange". Make sure this layer is above your "swan white" layer in the layers palette. You can now hide the "swan white" layer (click the eye icon to the left of the layer), we'll be using that again later... Adjust the colour on your "swan light orange" layer using Image/Adjustments/Colour Balance (Ctrl+B on a PC) and move the top slider into the red and the bottom slider into the yellow until the colour matches the orange of the sunset, like this:
From here we're going to keep adding layers on top of the existing layers, gradually darkening them, and erasing certain sections to reveal the lighter layers underneath.To do this, duplicate the "swan light orange" layer and call it "swan medium orange". Make sure it's above your "swan light orange" in the layers palette. Using both the Image/Adjustment/Colour Balance and the Image/Adjustment/Brightness and Contrast tools, adjust this layer so that it's a darker, deeper orange than the layer beneath it. Like this:
Now using a soft eraser set at about 45% opacity, start erasing the "swan medium orange" layer at the front of the swan, where the light hits it most brightly, to reveal the lighter swan underneath. When you're finished this, hide the "swan light orange" layer leaving only the "swan medium orange" layer visible. It should look like this:
Make both layers visible and then... (did you guess it?)... duplicate the "swan medium orange" layer and call it "swan dark orange" and repeat the same steps as above: - darken and deepen the orange colour using the Colour Balance and Brightness tools. - erase part of this new layer at the front revealing the lighter layer beneath it. If you hide the "swan light orange" and "swan medium orange" layers your "swan dark orange" layer should look something like this:
Once again turn on the layers underneath to reveal all three of your orange layers and you should have a swan that's gradually lit from light to dark orange, like this:
But there's a very vibrant blue in the sky that would also be reflected on the swan. This is where the original white swan layer comes back into play. Duplicate the "swan white" layer and call it "swan blue". Move this new layer to the top of your layers palatte so that it's above all your orange swan layers. Now again using the Image/Adjustments/Colour Balance tool use the sliders to change your white swan to a blue that's close the colour of the sky, like this:
Again using a soft eraser at about 45% opacity, start erasing parts of the blue layer to reaveal the orange underneath. Erase from the underside of the swan, where the orange light would reflect on him, leaving the blue at the top where the light from the sky would shine on him. You should end up with something like this:
But it's too bright, so now we'll use the Image/Adjustment/Brightness and Contrast tool and darken the "swan blue" layer to about -65. It should now look like this:
The blue is still a bit too overpowering, so reduce the opacity on the "swan blue" layer to about 60%, your layers palette will now look like this:
And your swan like this:
Now you can merge all the layers into one, but before you do that I'd suggest doing a "save as" and keep this version with the separated layers as a backup PSD file in case you want to come back and tweak it. I don't know about you, but I'm a notorious tweaker. Once you've created a backup copy, highlight all the swan layers and then select Layer/Merge Layers (Ctl+E on a PC) to merge them all into one layer. I then softened the edges in a few places using the "blur" tool, used the "clone stamp" to remove that odd black spot on the back of his neck, erased the bits on the tip of his left wing where the leaves should be in front and added some movement in the water. Here's the final version:
I hope this was helpful! Please don't hesitate to PM me if you have any qustions :D