Configuration | Colours

The colour of the PDF view background and the colour of the icons can be configured. You can see the default values here.

builder.Services.AddMudBlazorPdfViewer(opt =>
{
    // Set the icon colors
    opt.Colors.IconColor = Color.Secondary;
    
    // This can be any valid CSS color value (rgba, hex, etc.)
    opt.Colors.Background = "#000000";
});