Growing Shards

This is created by an algorithm inspired by fejesjoco (in the same challenge). Start with a black pixel in the center. For every pixel placed, mark the 8 surrounding pixels as available (if not already placed). Find one marked point by searching all pixels in the image in a specific order until a marked pixel is encountered. This specific order is a random permutation of all pixel positions. Every time all points are checked, the permutation is shuffled again. Then, calculate the average color of all placed pixels out of the 8 neighboring pixels. Find colors in the color cube that are not already taken and as close as possible to the calculated color. The closeness measure is the infinity norm (max(dr, dg, db); the skin of a cube). If multiple equally close colors are found, take the ones closest to black, using the negative-infinity norm (min(r, g, b)). If multiple of these are found, choose a random one. Place the found color at the found point.