As you may have notice, there are certain unique colors to each of the iterations. Colors aren’t chosen at random, they are the result of the following calculations. The first, last and middle letter of a word are assigned values according to this letter frequency chart (but in reverse, so that the least frequent letter has the highest value) then the values are mapped to a range of 0-255. First letter becomes the red component, second green third blue; this way a rgb value is defined for the whole word. Example here. I’ve drawn nine different patterns (which overlap in an interesting way, you can enable that in the source). Each pattern is assigned to a group of letters (smaller groups of often occurring letters and bigger of the rarer).

Source and more here