This tutorial was created using Adobe Photoshop CS, but it is working in any other similar graphic programmes.

Open your already shaded clothing item in your programme (to see how the shading's done, you can check this tutorial).

Make sure that there are two layers of the clothing item - one with the finished shading, and one without (only the outline and the filling).

Duplicate the shaded layer and name it "stripes".  Then pick the lasso tool  (setting as below) and select the stripes - take care to make the space between them as regular as you can.

Invert the selection (Shift+Ctrl+I) and delete the now selected area.
Now go to  Image > Adjust  > Hue/Saturation  to change the colour settings of the stripes.
You're done now! 

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