With the servitors I was able to get away from all the shiny metals, a bit. Like many commission models, these arrived already converted (a combination of Cryxian mechanithrall and space marine plasma arms). They make a simple and effective couple of fleshbots.
The marines all have some type of heraldry on their shoulders, so the servitors also have some identifiers in the form of a cog-rune device. The skin was done "borg-style" with greys and rotten flesh, complimented with mechanicum red. The plasma effect was done similar to the blades of the knights, light red to orange, which I think turned out ok.