[jQuery] Problems with $.addClass()

[rene.olivo]

Hello, I have tried this code:

$('#some_div').addClass('new_class');

And it works really well, it adds the class to the element. The
problem is that if this element had previously had any style applied
to it like:

#some_div {
   color: #F00;
}

to change the color with the new class I'd have to use !important so
it can be applied like this:

.new_class {
   color: #FFF !important;
}

does anyone knows why this happen? it works great and everything but I
rather not use the important statement if possible.

thanks.