Changing default colors in tkz-base

I've looked over the documentation and found, in tkz-base.cfg, the lines:

%<------   colors  ---------------------------------------–>
deftkz@backgroundcolor{white}
deftkz@textcolor{black}
%<---------------------------------------------------------
deftkz@fillcolor{tkz@backgroundcolor}
deftkz@mainlinecolor{tkz@textcolor}
deftkz@otherlinecolor{tkz@mainlinecolor!50}

We can change these colors by overwriting the definitions in the document. Because the color names contain the @ symbol we need makeatletter and makeatother, as follows:

Solution based on Marijn comment

documentclass[tikz,border=1cm]{standalone}

usepackage{tkz-fct}
usepackage{mismath}
usepackage{tikz-layers}

makeatletter
   deftkz@textcolor{white}
makeatother

begin{document}
    begin{tikzpicture}
        tkzInit[xmin=-5, xmax=5, ymin=-5, ymax=5]
        tkzDrawX[noticks, label=(Releft(zright)),below right,thick]
        tkzDrawY[noticks, label=(Imleft(zright)),thick]
        tkzDefPoints{0/0/O}tkzLabelPoints[below left](O)
        
        begin{scope}[on background layer]
            fill[black,opacity=.2,inner sep=2mm](current bounding box.north west) rectangle (current bounding box.south east);
        end{scope}
    end{tikzpicture}
end{document}