How do I completely change a color?

I'm wondering how I make a color completely different without making it look like I did anything. Like I'll see a picture of a car in 5 different colors and it's the same exact picture. How do I do that? Anyone have a link for me? I really don't know what to search for.

 

I have the perfect tutorial for you... and it works really really well.... just let me find it again.

edit: ok the tutorial is on a different hard drive that my stupid sister left at her friend's house.
I did a google search for "photoshop tutorial change car color" and heaps come up. But none are very good. Most just select the area you want to change the colour of by using a mask. Then fill with the desired colour and then change the blending mode.
This way doesn't look very good but it gets the job done.

I'll post up this other tutorial I have when I get it tomorrow... i can't remember all the steps off hand.

 

http://www.photoshopjunkie.com/tutorials/color2/index.htm

Get Busy!!

 

You can try just painting directly over it with the pencil blending mode set to color.

 

hue/sat adjustment layer and lots of masking.

 

Thanks fellas. Hey Xmetal, what kind of car is that? It has the front end of an Evo but it's a two door and the headlights aren't the same..