Color picker not changing text in select box

[eshops]

Hi,

Am hoping someone can help me on this strange behaviour I am experiencing with the color picker.
When I select a color the text in the seelct (drop down) box usually changes (it does on my test site, and on the prestashop demo).
For some reason on my production site, it is not doing this, and if I add a color SKU to the cart, it adds the wrong one.

Has anybody experienced this behaviour? Could it be something on the server that is making it bahave this way as test and prod site are the same?

thanks to anyone that can assit.
eshops!

[tomerg3]

Check the page for javascript errors (in Firefox->Tools->Error console).

[eshops]

Thanks tomerg3. My knowledge of the web and associated code is in its early stages. I wasnt even aware of this error console tool so thanks again, is handy to know that is available on the browser!

I cleared all messages and then viewed a product page and selected one of the color swatches, and again the select box text didnt change.
I checked the error messages after doing this, and the following error was recored:

id_color_default is not defined. then it mentioned the javascript program adn path...the program with the error is in the themes directory/js/product.js

If you have any advice on what may be causing this or how I can correct it I would be very appreciative.

regards
eshops!