I've got script that calls for a black dog - I have a trainer that has a large grey dog (the right price) and I'm wondering about making him black 'in post' - it doesn't have to look realistic - it's not a real dog, it's 'the black dog'.

I'm not sure if it's possible or where to start? - any suggestions?

Paint him.

Seriously. You can spray them with temporary hair dye, and wash it off later. Go to a makeup house and see what's available.

Can you rewrite the script to say "grey dog"? :-)

Otherwise Richard's idea might be the most practical. Talk to a stylist and a vet. Make sure the hair coloring won't hurt the dog's skin.

This could be done in AE with a mask and a curves and/or tint effect. I've done it, but it's a long process to mask in post depending on how much detail you want (DV vs HD or HDV, hair detail, etc). I would second temporary dye definitely, but if it absolutely can't be done it's possible (gruelling) to do it in post.

If you're working on a Mac you could also use Color for this using a secondary adjustment, but you'd have to be very conscious about the use and positioning of other colors in the frame.

Painting the dog is still much less of a hassle.

The trainer actually suggested a temp colour but I want to have a try at doing it in post first.

If the result is 'unrealistic' it may actually suit my purpose.

It's not 'a' black dog' - it's 'THE black dog' AKA depression so I really need a black dog to represent the illness. I want the audience to see the dog and then realise no-one else can, only the sufferer. Much like the illness it's very real to the sufferer and non-existant to those around them.

Vaguely related: I learned in art class years ago how to draw shadows on a black cat: create highlights.

You can apply this technique to your situation, hitting the canine talent with a point source which creates unnatural highlights. Even better if it's a perfectly jet-black dog and the hair has a gloss.

Again, you'll need to consult with a stylist.

Don't forget highlights in the eyes, and the fact that the retinas can reflect light straight back to the camera -- that can look unearthly, too.

Andrew Kramer at Video Copilot makes the video change to color in After Effects look pretty easy. I'm sure you'd need to adjust the tolerence to keep it where you want it but it seems like it would be the easiest way. Here's the link: VIDEO COPILOT | After Effects Tutorials & Post Production Tools (http://www.videocopilot.net/basic/tutorials/02.Effects/)
you have to get toward the end of the video to see the color change. Or maybe you could put the dog on a green screen, turn him black with the transparent background and then drop him into your video.

If "the black dog" is static maybe you could just use photoshop or mask it.

Hopefully that helps!