I have to do a RegionPlot of this strange function

func =  (x y)^2/z^2 Abs[1 - 1/(x)^2)] < 1/(210)^2;

I do it with

Plot = RegionPlot[funct  /. z -> 10, {x, -1, 1}, {y, -1, 1}, PerformanceGoal -> "Quality", PlotPoints -> 250, BoundaryStyle -> None]

where I needed the PerformanceFoal and PlotPoints to improve the quality of my plot.

Now, I have to overlap plots of this kind for different values of $z$ but I am not sure of the set of color to use, I would like to just change the color at the end, when I'll do the Overlap[...] or Show[...]

Mathematica takes 13 secs to do the plot. I

Is there a way to let Mathematica process the points of the plot once for all and then change quickly the color without wasting 13 secs of my time everytime I want just to change the color?

I hope my question is clear.