enamel has the downside of being hard to paint over or get any other paint to adhere to. I'd recommend a primer in something simple like
GW's chaos black or Armoury's black. armoury has a upside of leaving a fine enough grit to soak up the first base coat very well and leave your model either very bright or very dull depending on the base coat or subsequent coats. you Just wants fast and easy ...well the easyest way is to use a prime coat in your primary color and then paint the armor in the secondary color and Dip it. let dry and varnish and a coat of matte and yer done.
an example of such from my old tyranid army
bleach bone prime, dry brush bleach, paint armour dark angel green and paint teeth and eyes and dipped in minwax.