Aviation Academy Graduate Badges, what is the significance of the colour ?

[plmurphy]

I have a number of graduate badges in my collection all to what I believe is the State Aviation Academy (feel free to correct me if I have the name incorrect). So far I have the same badge in navy, red, and yellow. I am also aware of a pale blue version. Does anybody know which disciplines are represented by the different colours ? Pale blue, for example, normally represents pedagogical studies but that is hardly the case for an aviation academy !

The badges are attached for those who are interested. First up, the navy version.