Aculture medium on which only gram-positive organisms grow and a yellow halo surrounds staphylococcus aureus colonies is called a(n)

I believe the most appropriate is a selective medium and differential medium. Selective medium types are formulated to support the growth of one group of organism, but inhibit the growth of another. Blood agar is a differential medium that distinguishes bacterial species by their ability to break down the red blood cells included in the media. Blood agar is often used to distinguish between the different species of pathogenic streptococcus bacteria.