How do I reset or override IE CSS filters?

try this:

filter: -;

The -ms-filter property is a non-standard, browser-specific CSS entry and as such requires that its parameter is enclosed with quotation marks. So -ms-filter: "none" will work just fine.

There is boolean attribute enabled, for which you can set false or true http://msdn.microsoft.com/en-us/library/ms532997%28v=vs.85%29.aspx

Example:

-ms-filter: "progid:DXImageTransform.Microsoft.gradient(enabled=false)";