Yes, it is colour mixing. Kodachrome is slide transparency film. So transmitted colours are mixed.
Originally Posted by Mustafa Umut Sarac
In a colour monitor, Red, Green, and Blue light (relatively narrow bands of frequencies) are mixed to make colours, because transmitted colour is Additive. We perceive Yellow when Red and Green light are mixed. We also perceive Yellow when light in the yellow frequency range is radiated. This means that there are several combinations available to produce many colours. This is called "metamerism" and uses "metamers".
In printed material, colour is reflected and so it is subtractive. Yellow is part of the CMY primary colours. It reflects yellow light. Just how that is constituted depends on the actual ink used.
In a transparency film, colour is produced by filtration, so it is subtractive. The filter subtracts (blocks) light. White light has all frequencies (all colours). The white light of the light table or projector is filtered by the slide. Where the Yellow layer and the Magenta layer are both present (have Y and M tones in that area) they together filter out light to give the perception of Red.