here is mine:
silver: 50/50 black/shadow grey, highlight by adding white.
bluish steel: 50/50 shadow grey/codex grey. shade with 50/50 mix plus black, highlight with mix plus white.
gold: scorched brown, snakebite leather, leprous brown (this is an old one, but 50/50 snakebite and yellow will work) golden yellow, white.
bronze: scorched brown, bestial brown, beastial brown plus white.
look at my gallery for some examples (my alahel the messenger, from rackham, has all 4 of these on it.)
hope this helps
-matt