Plotting functions using domain coloring

Not sure if this is what you are looking for but you can use existing diagrams and import them in pgfplpots. Then you can use the normal tikz commands and pgfplots commands to prettify your plot.

This plot type allows to extend the plotting capabilities of pgfplots beyond its own limitations. The idea is to generate the graphics as such (for example, a contour plot, a complicated shaded surface9 or a large point cluster) with an external program like Matlab or gnuplot. The graphics, however, should not contain an axis or descriptions. Then, we use includegraphics and a pgfplots axis which fits exactly on top of the imported graphics

-- Taken from the pgfplots manual: 4.3.7 Using External Graphics as Plot Sources.

documentclass{article}
usepackage{graphicx}

usepackage{pgfplots}
pgfplotsset{width=7cm,compat=1.15}

begin{document}
% See also https://tex.stackexchange.com/questions/231738 for "example-grid-100x100pt"
% See pgfplots manuel "4.3.7 Using External Graphics as Plot Sources" including "Support for External Three-Dimensional Graphics" 

begin{tikzpicture}
begin{axis}[
enlargelimits=false,
axis on top,
]
addplot graphics [
xmin=-3,xmax=3,
ymin=-3,ymax=3,
] {example-grid-100x100pt};
end{axis}
end{tikzpicture}

end{document}

-- Taken from the pgfplots manual.