Heres the full answer:
clc;
ax=app.UIAxes;
b=ax.Children; % b(1) is last object added to uiaxes
n=numel(b);
ReportMessage(app,'******* Graphics Objects [RGB] (1=newest) *******');
for i=1:n
T=b(i).Type; % Get object type (i.e. line, text)
C=b(i).Color; % Get colour of object [R G B] format
ReportMessage(app,[num2str(i),': ',T,', color: ',num2str(C)]);
end
drawnow;