BackgroundColorResource.Color

public Color Color { get; set; }

[C#]

string sourceFilePath = "input.psd";
string outputFilePath = "output.psd";

using (var image = (PsdImage)Image.Load(sourceFilePath))
{
    ResourceBlock[] imageResources = image.ImageResources;
    BackgroundColorResource backgroundColorResource = null;
    foreach (var imageResource in imageResources)
    {
        if (imageResource is BackgroundColorResource)
        {
            backgroundColorResource = (BackgroundColorResource)imageResource;
            break;
        }
    }

    // uppdatera BackgroundColorResource
    backgroundColorResource.Color = Color.DarkRed;

    image.Save(outputFilePath);
}