Minor mode for colouring plain tex lowercase greek letters

[michael-franzese]

Am trying to write a minor made to highlight tex keywords.  I am starting
with the lowercase greek letters: \alpha, \beta, \gamma, \delta, \epsilon,
\zeta, \eta, \theta, \iota, \kappa, \lambda, \mu, \nu, \xi.

Do not know how I can set the lowercase greek letters to some colour.

I would have to assign a face to each regexp group rather than defining my own 
faces.
Reuse the font-lock faces that one can find on M-x find-library RET faces RET.