The two pages of https://github.com/HiraokaHyperTools/SampleXpsDocuments_1_0/raw/refs/heads/master/Handcrafted/ColorTransparency.xps should be identical, at least according to what the authors of the file wrote. However, for each square S of a light color “Light C” on the first page, MuPDF draws an open square inside S that is only a tiny bit smaller than S and that has an edge of the color C, whereas on the second page, such internal squares are not drawn. Either the authors of ColorTransparency.xps were wrong with respect to the XPS specification, or MuPDF doesn't do a good job on rendering the file. (The second is likely to be the case, as the original file is from the XPS folks at Microsoft.)