AnisotropyDiscTest blue channel fix

[echadwick-artist]

Fix for issue #44

• Blue channel edited so the outside of each circle is zero black.
• Inside the circle of the bottom left quadrant, the blue channel values have been scaled down so the gradient starts at zero black on the edges of the circle, ramping up to white at the center.
• Screenshot updated.

[echadwick-artist]

Committing this since it has been 2 weeks and there are no concerns.