Variables in coloring formulas

Is there any way to make formula variables visible in the coloring formula loop? I'm trying some fractals with more than one variable z and need to use both in coloring.

I have an ugly workaround basically doing all the coloring in the fractal formula and stuffing the color index in #z at the end and then just setting #index = #z in the coloring formula.

There's no other way to do it. An alternative is to use the standard Pixel formula, and have your coloring algorithm do both the fractal formula calculations and the coloring.