Plotting Lines of Different Colors

I'm plotting the thermal efficiency vs. pressure ratio of an engine based on varying pressure ratio and turbine inlet temperature. I'm coming up with multiple lines of constant temperature on my plot. They're all coming out in blue because of the way I coded it however. If anyone knows how I can change their colors automatically instead of changing my code and going through one by one, that would be awesome.

clear all; close all; clc;

%Defining known values
T3=1100;
nT=0.89;
nC=0.84;
T1=290;
P1=101.325;
k=1.4;

% Overall Efficiency: nth=1-(T1/T3)*((rp)^((k-1)/k))

%%Varying Only Pressure Ratio

rp(1)=0;
i=1;

while rp<=30
    nth(i)=1-(T1/T3)*((rp(i)^((k-1)/k)));
    i=i+1;
    rp(i)=rp(i-1)+0.1;
end
nth(i)=1-(T1/T3)*((rp(i)^((k-1)/k)));
plot(rp,nth);

%%Varying Pressure Ratio and Turbine Inlet Temperature

figure;
T3=800;

while T3<=1500
    rp=0;
    nth=0;
    i=1;
    while rp<=30
        nth(i)=1-(T1/T3)*((rp(i)^((k-1)/k)));
        i=i+1;
        rp(i)=rp(i-1)+0.1;
    end
    nth(i)=1-(T1/T3)*((rp(i)^((k-1)/k)));
    plot(rp,nth);
    hold on;
    T3=T3+100;
end

grid on;
title('Varying Turbine Inlet Temperature');
xlabel('Pressure Ratio, r_p');
ylabel('Thermal Efficiency, \eta_t_h');
legend('800K','900K','1000K','1100K','1200K','1300K','1400K','1500K');

The "Varying Turbine Inlet Temperature" is the plot I am interested in.

Answer 1

[Jiro Doke]

Here are a few pointers:

1. To use the auto coloring with plot, use hold all instead of hold on.
2. The default ColorOrder has only 7 colors. This means that after 7 lines, the color repeats. To have more colors, change the ColorOrder of the axes to have more color (in the form of m-by-3 matrix of RGB values).
3. There are some preset colormaps that you can use. For example, you can create 8 colors that span the JET colormap by using the command jet(8).

The key lies in the two lines after the figure command below.

clear all; close all; clc;
%Defining known values
T1=290;
T3=800;
k=1.4;

%%Varying Pressure Ratio and Turbine Inlet Temperature
figure; 
set(gca, 'ColorOrder', jet(8));
hold all
while T3<=1500
    rp=0;
    nth=0;
    i=1;
    while rp<=30
        nth(i)=1-(T1/T3)*((rp(i)^((k-1)/k)));
        i=i+1;
        rp(i)=rp(i-1)+0.1;
    end
    nth(i)=1-(T1/T3)*((rp(i)^((k-1)/k)));
    plot(rp,nth);
    T3=T3+100;
end
grid on;
title('Varying Turbine Inlet Temperature');
xlabel('Pressure Ratio, r_p');
ylabel('Thermal Efficiency, \eta_t_h');
legend('800K','900K','1000K','1100K','1200K','1300K','1400K','1500K');

[Jeremy]

Thanks, worked like a charm. I couldn't get it to work at first and I realized I forgot to take the hold on out.