Open the document you want to change the color of. Remember to make a back up of the original.

Select the area of color that you wish to alter, in this case, the girl's T-Shirt. Use a combination of the Lasso and Extract tools.

To make an accurate selection, zoom in on the image, to about 800%, then select the polygonal lasso tool.

With the polygonal lasso tool, make your selection by clicking around the target's edges.

Continue clicking around the edges until you come back to the beginning to end the loop. If you have multiple area you want to select, then hold down SHIFT then start making another selection, this will add the next selection to your current one.

Dont worry too much if you accidently go outside or select unwanted area. We can fix this later.

Once you have your selection, zoom back to 100%.

Now click on the quick mask button, this is the right button located just below the colors.

Now you will see something similar to mine below, your selected area in normal colors, and the rest (un selected area) in transparent red. This is quick mask mode.

Now make sure your colors are set to black and white, select the "paint brush" tool and set the brush size to 13 hard edge.

Now if you "paint" over your image with BLACK, it adds to the selection, and if you paint in WHITE, it DELETE from the selection. with this in mind, zoom in on the image and find spots that you missed or are not accurate and paint accordingly.

if you look at my image below, my selection using the lasso tool was not perfect, so I use the brush tool now, and color in where I missed.

Tip: press "X" to change alternate the black and white colors.

If the brush size is too big, change it to smaller brush to get into tight areas. But remember to use hard edge brushes, as soft edge will give you inaccurate results.

This is how it look after I paint over the area with black.

Do this for your whole image to get accurate selection.

Another way to change color of the selection is using variations function Image » Adjustments » Variation.

This enables you to easily add shades of colour to highlights, midtones or shadows and is a useful means of creating new tones. Unfortunately, it lacks the subtlety of other methods.