Tricky Photoshop / other graphics app problem - how to?

Hello,
wondering if someone could explain how RL have managed to fill a defined area of clothing with a texture or colour.

Please see:

http://www.ralphlauren.com/product/index.jsp?productId=3064569&cp=1760781.2708576&ab=ln_men_cs10_createyourown&parentPage=family

You can see as the user selects a fabric colour, the image with the model updates with the chosen texture. I know basic colours can be done easily by using a hue/saturation layer and adjusting until you get the desired effect. However, I'm unsure how they have managed to fill the selection with the textures/stripes that they have - unless of course the original model photo was shot wearing a striped polo shirt.

More generally: if I want to fill a selection of a tshirt accurately (complies with direction, contours of clothing, shades/tones, etc) with a series of textures that I have, how can it be done? I'v been using PS for years, but I don't know how to do this. Can this be done at all in PS? If not, what technique in what application would be most suitable for this job?
Thanks a lot for any help.
dela.