This style re-colors DuckDuckGo's logo and other branded elements in the page (three options leave the logo unaltered!). It does not replace any artwork, nor it changes the page design in any other way. If the layout of the search results in some screenshots differs form the usual layout, it is because of having DuckDuckGo - Multi-Columns Custom style enabled in those samples.

The style changes the color of the duck's disk, the page top border, the search button, the tab titles for the Instant Answers, the scroll buttons for those answers, the rating stars, and the Official Site badge. All those are changed from orange (or green in the case of the search button) to whichever color you choose (the White over Orange option makes the search button orange). The Plain White option sets DuckDuckGo's unaltered logo with clear background but it also makes some of those changes that DuckDuckGo alone does not; and the Plain Black option is its complement. The options for White Duck Only and Black Duck Only do not change anything but DuckDuckGo's logo.

This style will not change the page background color. This can be achieved easily through DuckDuckGo's https://duckduckgo.com/settings, in the Appearance tab (you must allow DuckDuckGo's permanent cookies for this to work properly). Is best to do this before applying the style. I suggest to change the background color for both the page and the header to the same color. Note that when you change the background color, DuckDuckGo adjusts the color of almost everything else accordingly, including the text color. My advice is to use a background color that is very light or very dark with low saturation; that way the text will look either white or black. I find good results with these values: dark gray #181818, dark marron #221111, dark blue #111122, dark purple #221322, dark teal #081b1b, light pink #fcf2f2, light green #eefdee, pale turquoise #afeeee, and light tan #e9e0cf. After you change the background color, you can choose a matching duck with this style.

The style options Black over White, Black over Gold, and Plain White should be used with a dark background, otherwise the Instant Answers tab titles and the stars become hard to read. Complementary, the style options White over Black, and Plain Black should be used with a light colored background.