The following paper, "Junction temperature in light-emitting diodes assessed by different methods," characterizes LED tempco for various LED colors and uses the measurement of delta-Vf (the change in forward voltage resulting from tempco) to indirectly determine junction temperature. As bias sources, we benefit for the work of S. Chhajed, Y. Xi, Th. Gessmann, J.-Q. Xi, J. M. Shah, J. K. Kim, and E. F. Schubert of the Rensselaer Polytechnic Institute.
https://www.ka-electronics.com/Images/p ... Tempco.pdf
"The coefficient dVf /dT is equal to – 2.3 mV/K for the UV LED sample (? = 375 nm), – 5 mV/K for the blue LED sample (? = 455 nm), – 3.8 mV/K for the green LED sample (? = 530 nm), and – 1.5 mV/K for the red LED sample (? = 605 nm)."