Well
GW has confirmed that we in fact have 5 companies, not 4 like most believe. Oh and they the third company's blood drop red which is nice as it's supposed to be set on a white arrow/cross/explosion. I'm not certain where the 4 companies idea came from but i see it everywhere and my guess is that when it was first said they were not taking into account the first company (Veterans).
Picture from the black library Flesh Tearers Supplement: