Generate F.M signal and develop the T-F spectrum of the signal. Hence interpret the T-F spectrum.I am looking for the interpretation of the T-F diagram.My query is what does the color differences mean and why the spectrogram is like scratches?

%assignment 4.2

%creating a multitone modulating signal

Fs=1000;%16khz

Fc=200;%carrier frequency =5khz

Ts=1/Fs;

t=0:Ts:0.3;

x=sin(2*pi*30*t)+0.2*sin(2*pi*60*t);

freq_dev=50;

s_t=fmmod(x,Fc,Fs,freq_dev);

plot(t,x,'c',t,s_t,'k')

xlabel('Amplitude');

ylabel('time(sec)');

f=figure();

colormap(f,jet);

spectrogram(s_t,256,0,[],Fs,'yaxis')

% figure();

% z=fmdemod(y,Fc,Fs,freq_dev);

% plot(t,z,'r--')