Prime Diamonds builds on ideas from ColorCompass.

Working on the sum rule from the green part of ColorCompass, I took the 
absolute values of x and y prior to summing them, which if I'm correct, 
should result, not in a diagonal gradient, but a square one that is 
rotated 45-degrees to the grid.

If I simply left all three color channels as a plain square gradient, I 
would just end up with a grayscale, so to add some variety, I take the 
sum of the coordinates and divide it by the primes 2, 3, and 5. If the 
sum is a multiple of 2, that pixel gets red, a multiple of 3, it gets 
green, and if its a multiple of 5, it gets blue.

This should result in a multicolor pattern of concentric squares, of 
red, green, and blue for numbers with only one of 2, 3, or 5 in their 
prime facterization, yellow, cyan, and magenta for numbers with two of 
2, 3, and 5 in their prime factorization, and gray for numbers that are 
multiples of 30(The least common multiple of 2, 3, and 5, with black for 
1 and all numbers with 7 as their smallest prime factor.

The intensity is based on taking the remainder of the x+y sum divided by 
255, allowing the image to extend beyond a small patch, and which should 
result in concentric bands that brighten from their inner edge moving 
outward.

primeSquare is the unmodified version with all three channels having the 
same base formula.

primeError was an attempt to stretch the red and blue channels into more 
elongated rhombi, one vertically, the other horizontally, but after 
generating the image, I realized the logic should affect brightness, but 
not the shape of the blue and red parts of the pattern. The transformation 
here is to do the prime division test on the sum, but set intensity 
based on doubling one of x and y in the sum.

primeDiamonds is a second attempt to stretch the red and blue parts of 
the pattern. This time, x or y is doubled during the summation, and if 
the sum is divisible by the correct prime, it is modded by 255 to 
determine the intensity.