fig1.text(0.365, 0.62, '$e^{-x/5}$', ha='center', va='bottom', size=
    'medium', color='blue')
fig1.text(0.412, 0.62, '$e^{-x/1}$', ha='center', va='bottom', size=
    'medium', color='green')
matplotlib two different colors in the same annotate