How to change colours

I have seen many a picture where it has been changed to black and white and only one chosen colour stays the same. Or sometimes it can be changed. In the photo below she was originally in normal colour and the bikini was blue. I would really love to do this with some shots of my wife but cant get the colour to work. I have asked the person who did this and he didnt want to tell me. Any help guys???

Check out this thread

http://forum.teamphotoshop.com/showthread.php?t=25927&highlight=black+white

I do lots of colorizations meaning I take images that are completely desaturated and add color to everything including the background.

For what you seem to need, that isn't necessary. If your picture is in color, duplicate the image and desaturate it then in a new window, make sure the desaturated layer is below the color one. Then, use quick mask mode on the color layer and select a soft round brush, one of the preset ones should do fine. Paint over what you want changed. You'll know you're in quick mask mode by the foreground color being black and background color being white as soon as you click the quick mask button located at the bottom of your layers palette. It's the square with the circle in the middle. What makes quick mask so good is that if you paint something you don't want, you can undo it by using white instead of black. Black paints the area you want to alter, white erases it. That way if you make a mistake, you can go back.

Once you paint the area, you can go to Layers > Adjustment Layer > Color Balance. Manipulate the color to something you want or close to it. After that, you can make another adjustment layer or layers by using Selective Coloring because Color Balance isn't the ideal way to add color.

Now, once you've painted what you want, right-click the last layer which will likely be an adjustment layer, right-click and "set selection to layer mask" and you'll see that what you painted is now selectied. Make sure you press Shift-Command-C unless you want to flatten the layers and then all you do is paste it on your original color picture and it will overlap the area you wanted. If anything overlaps too much, you can always erase it by using the eraser tool or adding a layer mask.

If you'd like a full-on tute, I can fetch one for you. If you want to color more than one area, use your selection tool and make a fill layer and more adjustment layers or use the quick mask mode again, making sure to save often.

Once you do it a few times, they're easy.

in photoshop7 select _ Colour Range does a good trick of isolating colours. duplicate layer, take top layer - select colour range bikini, then select - invert, and clear everything but bikini, then desaturate the lower layer

Meh, I used to have Gimp and the last time I've done a colorization or soemthing else liek that was in Gimp. So I'm not really sure how to do it in Photoshop, but I can tell you WHAT to do: If you want a desausteration with only a bit of color here and there (That car was a nice one) then you duplicate the layer, desausterate it, then you 1) duplicate the original too and bring it to the top. Then erase the sections which you wish to stay black and white. Or, the simpler way: 2) then taking the eraser and erase the sections i nthe desausterated layer which you want to stay colored.

For changing colors, Go to layer>new adjustment layer>selective colors or color balance. Either one usually works, unless you're selecting a FLAT COLOR (Liek the bikini was flat blue) then I suggest you use the selective colors plug-in. Click okay then choose which color tone you would like to change (in this case blue). Then adjust the settings for 'til you get the color you like!

Hope this helped!