Option 1: use a legend for the codes and a colorbar for the continuous data
The easiest and cleanest method might be to set a different black symbol for each code and to define those symbols within a legend. Then use a colorbar to define the continuous data.
Here's an example just to give a picture of what this may look like.
% Create data
data = randi(101,1,200)-1;
dataMat = reshape(data(randperm(numel(data))),10,[]);
[x,y] = meshgrid(1:size(dataMat,2), 1:size(dataMat,1));
% insert some code values
uniqueCodes = [200,201,202,203];
codeSymbols = {'s','d','^','p'}; % 1 symbol for each code
codeIdx = unique(randi(numel(dataMat),1,30));
codeIdx = ismember(1:numel(dataMat), codeIdx);
dataMat(codeIdx) = randsample(uniqueCodes,sum(codeIdx),true);
% Plot the data, not the code
fig = figure();
ax = axes(fig);
hold(ax,'on')
h1 = scatter(ax, x(~codeIdx),y(~codeIdx),50,dataMat(~codeIdx),'filled');
% Add codes symbols
h2 = arrayfun(@(i)scatter(ax, x(dataMat==uniqueCodes(i)),y(dataMat==uniqueCodes(i)),70,'k','filled','marker',codeSymbols{i}),1:numel(uniqueCodes));
% add colorbar and legend
colorbar()
legend(h2, compose('Code %d',uniqueCodes))
Option 2: Add blocks of discrete colors to a continuous colorbar
This can get complicated. The inline comments in the demo below provide more detail but the main idea is to scale the colorbar so the top ~25% of it is devoted to a discrete set of colors. Then scale the data and the code values to fit the sections of the colorbar.
% Create a grid of data points
data = [randi(101,1,200)-1, randi(4,1,10)+199];
dataMat = reshape(data(randperm(numel(data))),10,21);
[x,y] = meshgrid(1:size(dataMat,2), 1:size(dataMat,1));
% Define codes and their colors
uniqueCodes = [200,201,202,203]; % list unique codes
codeColors = [... % Define 1 color per code
1.0000 .75000 .79297; % pink
1.0000 .41016 .70313; % hotpink
1.0000 .00000 .00000; % red
.54297 .00000 .00000]; % darkred
% Define colormap for the range of data
cm = parula(256);
% Devote the top ~25% of the colorbar to the code-colors
nCodes = numel(uniqueCodes);
rowsPerCode = round((size(cm,1)*.25) / nCodes);
codeColorsRep = repelem(codeColors, rowsPerCode, 1);
cm(end-size(codeColorsRep,1)+1:end,:) = codeColorsRep;
% Assign colormap and colorbar to plot (still no data plotted)
fig = figure();
ax = axes(fig);
ax.Colormap = cm;
cb = colorbar(ax);
% Use caxis to scale the color range so that the continuous part spans the min-max of your data
dataLimits = [0,100]; % <----- You'll have to calculate this; it's the min,max of your data (ignoring the code values)
continuousPortion = (1-size(codeColorsRep,1)/size(cm,1));
cblim = [dataLimits(1), ceil(dataLimits(2)./continuousPortion)];
caxis(cblim)
% Compute centers of each code-section in the colorbar
discreteTicks = linspace(range(cblim)*continuousPortion+cblim(1), cblim(2), nCodes*2+1);
discreteTicks(1:2:end) = [];
% Set colorbar ticks
cb.Ticks = [0 : 10 : dataLimits(2), discreteTicks];
% Set tick lables
cbTickLab = cb.TickLabels;
cbTickLab(end-nCodes+1:end) = compose('Code %d',uniqueCodes);
cb.TickLabels = cbTickLab;
% Replace code-values with the colorbar tick values
for i = 1:nCodes
dataMat(dataMat == uniqueCodes(i)) = discreteTicks(i);
end
% Plot the data
hold(ax,'on') % important, otherwise you'll lose the colorbar etc.
sh = scatter(ax, x(:),y(:),50,dataMat(:),'filled');
Option 3: Create 2 colorbars using a 2nd invisible axes
% define code values
uniqueCodes = [200,201,202,203];
% Define code colors
codeColors = [... % Define 1 color per code
1.0000 .75000 .79297; % pink
1.0000 .41016 .70313; % hotpink
1.0000 .00000 .00000; % red
.54297 .00000 .00000]; % darkred
% Plot the data, not the code
fig = figure();
ax = axes(fig);
% plot here......
% Add 2nd invisible axes
ax2 = axes('Visible','off');
linkprop([ax,ax2],'position')
% Set colormap to ax2
ax2.Colormap = codeColors;
% add colorbars
cb1 = colorbar(ax);
cb2 = colorbar(ax2);
% Reposition axes
ax.Position(1) = ax.Position(1)*.8;
ax.Position(3) = ax.Position(3)*.8;
% Reposition colorbars
cb2.Position(1) = sum(cb1.Position([1,3]))+.1;
cb2.Ticks = linspace(0,1,numel(uniqueCodes)*2+1);
tickLabels = cell(1,numel(cb2.Ticks));
tickLabels(2:2:end) = num2cell(uniqueCodes);
cb2.TickLabels = tickLabels;
