Configuration | Colours

The colour of the PDF background, toolbar and icons can be overridden with your preferred values. You can see the default values here.

builder.Services.AddBlazorPdfViewer(opt =>
{
    // Hot dog stand theme
    opt.Colors.Toolbar = "#000";
    opt.Colors.Icon = "#FF0000";
    opt.Colors.Background = "#FFFF00";
});

The above code will produce the following output;