There are two ways to notice that the color of the search icon in Vector skin (the magnifying glass on the right in the search field on the top of every page) is slightly different depending on whether JS is active or not:
Either you open a page with JS enabled, and a second time with JS disabled and switch between the two tabs. You'll notice that the non-JS version is a bit darker.
Or you watch the icon while loading the page. The icon is initially shown in the non-JS version and gets a bit lighter when JS has finished loading, causing a little flash.
That flash is the reason why the icon should have the same color both in the JS- and in the non-JS-version.