To superimpose plots with different colormaps, I have to plot them to separate axes and then assign different colormaps to the separate axes. However, the axes have an opaque background. I just checked the documentation for axes(), and although there are properties for transparency, they're currently unused because that functionality has not been implemented yet. I guess that means I need to find another way.
For completeness, here's the code that overlays two axes objects with different colormaps, but will not work for my purposes because they're opaque.
blue = [0,0,1];
red = [1,0,0];
green = [0,1,0];
orange = [1,0.5,0];
purple = [0.75,0,0.75];
discrete_clrmp = [blue;red;green;orange];
redblue_clrmp = [linspace(0,1,100)',zeros(100,1),fliplr(linspace(0,1,100))'];
orangepurple_clrmp = [fliplr(linspace(0,1,100))',fliplr(linspace(0,0.5,100))',linspace(0,0.75,100)'];
fig = figure(3);
ax1 = axes(fig);
ax2 = axes(fig);
data = "">pcolor(ax1,data);
continuousdata = rand(23);