Various shades of blue's functions

We discuss random matrix models in terms of elementary operations on Blue's functions (functional inverse of Green's functions). We show that such a description encapsulates the essence of a number of physical phenomena whether at/or away from the critical points and provides an elegant way for discussing them. We illustrate these assertions by borrowing on a number of recent results in effective QCD in vacuum and matter, as well as effective quantum systems of disorder with strong or weak dissipation (Hatano-Nelson localization). (author)