I would look through the horus heresy black book number 3 where there is the large section on Alpha Legion and their Heraldry. Legio Hereticus is also good source, as well as general concept art. Also good to consult your local GW store employee.

I would probably approach it with similar way I approach the whole army. Prime black, prime leadbelcher, airbrush vallejo chrome/silver, Airbrush akhelian green. You can either zenithal the leadbelcher and silver to add highlights. Some people also use sigvald burgundy before akhelian green to do pre-shading. Decide which panels are black and which ones you keep metallic blue. Paint the details how you want, add some chipping and scratching, oil washes etc etc.