Can Photoshop Create Everything the Mind Imagines?

This is a simple studio image of Abigail in front of a white seamless background:

My vision here was pretty simple. In my mind, replacing the white background with a deep blue background, similar to the color of her jumpsuit, would be nice. Over that, I would place a bright yellow oval, then blur it to fade it into the blue for a nice halo effect. Here is the result:

The murky greenish tint between the blue and yellow is not what I had in mind! But yellow and blue are primary colors. Mixing them together results in the secondary color of green. I can imagine a smooth, gradual blue to yellow transition with no green, but could not achieve it in Photoshop. To reduce the green, I choose a lighter shade of blue. This is not quite what I wanted, but a decent compromise: