Branko Grünbaum and G.C. Shephard in their book Tilings and patterns gave an assessment of previous work in the field. Commenting on Color and Symmetry they said:"Loeb gives an original, interesting and satisfactory account of the 2-color groups... unfortunately when discussing multicolor patterns, Loeb restricts the admissible color changes so severely that he obtains a total of only 54 periodic k -color configurations with k ≥ 3." Later authors determined that the total number of k -color configurations with 3 ≤ k ≤ 12 is 751.