Interesting observation. The blue flame color of all hydrocarbon fuels is due to the emission small diatomic carbon species such $C_2$ or CH. There is nothing magical about IPA having a yellow flame. The yellow flame originates from incomplete combustion. There is more carbon per mole of IPA as compared to ethanol. Yellow flames are called reducing flames and blue flames are called oxidizing flames.
In older times when Bunsen burner was taught in detail, it was shown a blue flame of methane can be readily converted in to a yellow flame by altering the air supply valve. The yellow color, if you view through a spectroscope is a continuous spectrum (rainbow like), which shows that it is like a black body radiator. The black body radiator is nothing but glowing soot (carbon) particle, glowing chrcoal but a very small one. On the other hand, the blue flame shows band like structure. I once had a chance to view the blue acetylene flame with air with a diffraction grating. It was an amazing sight. The structure of colored bands was never seen before. They are called Swan bands. Unfortunately, I cannot find any color images in Google Images of Swan bands.
Here is one example from a 1857 paper by Plucker and Hittrof, "I. On the spectra of ignited gases and vapours, with especial regard to the different spectra of the same elementary gaseous substance". This more than 150 year old picture is not doing justice to what you see in reality of an extremely beautiful spectrum.