The difficulty is that the coloring formulas only have access to the series of z values generated by the fractal formula. Thus the fractal formula has to keep track of the true z within itself, do some extra calculations, and store the needed result in z for the coloring formula to use in its summation. Something similar is done with various Slope fractal formulas, as in dmj.ufm and reb.ufm.

Thus one would have to write a cooperating pair, fractal formula and coloring formula.

The difficulty is that the coloring formulas only have access to the series of z values generated by the fractal formula. Thus the fractal formula has to keep track of the true z within itself, do some extra calculations, and store the needed result in z for the coloring formula to use in its summation. Something similar is done with various Slope fractal formulas, as in dmj.ufm and reb.ufm.
Thus one would have to write a cooperating pair, fractal formula and coloring formula.