See the gray bar in this example page:
Here is my attempt at recreating that gradient using CSS3 – also using CSS3PIE:
#navigation {
border: 1px solid #888888;
border-radius: 22px;
-moz-border-radius: 22px;
-webkit-border-radius: 22px;
height: 50px;
font-family: Arial;
background: #AAAAAA;
background: -webkit-gradient(linear, 0 0, 0 bottom, from(#AAAAAA), to(#757575));
background: -webkit-linear-gradient(#AAAAAA, #757575);
background: -moz-linear-gradient(#AAAAAA, #757575);
background: -ms-linear-gradient(#AAAAAA, #757575);
background: -o-linear-gradient(#AAAAAA, #757575);
background: linear-gradient(#AAAAAA, #757575);
-pie-background: linear-gradient(#AAAAAA, #757575);
behavior: url(/Public/stylesheets/PIE.htc);
}
This result in:

How can I reduce the bleeding effect, so the color transition is harder?
Have a white gradient fading in opacity up to 50% over your desired background color. This method can be used on any background color without changing the gradient CSS.
Demo: http://jsfiddle.net/ThinkingStiff/Zn5Qb/
CSS:
HTML:
Output: