Changing the Form disable colours in CSS

I've found a way to disable a form input if a certain checkbox is checked
using JavaScript, but is there anyway to change the colours that are used
when it is disabled?
Or alternatively, being able to set a form input to disabled and change the
class in the style sheet that it uses.

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So basically;
If 'forminput1' is checked then use class 'newclass' and disable
else use class 'oldclass'
I'm sure you won't find this in any programming language script
specifications :-)
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There probably is a way to do it but I'm not good enough a JavaScript to be
able to figure it out yet.

Thanks in advance.

Ben Bradley UK
Creative Director
http://www.thenetzone.co.uk

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