The main difference between yellow grapefruit and ruby red grapefruit lies in their color and flavor profiles: Yellow grapefruit, also known as white grapefruit, has a pale yellow skin with a hint of green. The flesh inside is typically pale yellow to light pink. On the other hand, ruby red grapefruit has a vibrant red or pinkish-red flesh, often with a deeper red color closer to the peel. Yellow grapefruit tends to have a tangy and slightly bitter taste with a hint of sweetness. It is known for its refreshing and tart flavor. Ruby red grapefruit, on the other hand, is generally sweeter with a milder acidity. It offers a pleasant balance of sweetness and tartness, making it a popular choice for those who prefer a sweeter citrus taste.