Looking good so far, i'm really liking the osl on the termies. Any chance of seeing them on a white background so that it's easier to make out what is osl and what is actual ambient lighting. Kudos on some great poses for the army, it's always nice to see marines posed ready for action.
Now to this guy,
I'll be honest i think that the problems you are having with working through the paint scheme on this is more down to the model than anything. The problem is that you've removed some chaos markings but not all and that the details you've added on are reasonably large and heavy. Compare the blood drop on the right shoulder with the chaos star on his right knee and you'll see what i mean.
Some of the biological elements on the model you might have gotten away with painting up as mechanical (painting the six pack on the chest and area around the termi head gold for example to mimic sanguinary guard armour for example) but other aspects are always going to look chaotic. The spikes on the armour trim and bio mass around the shoulders are going to look like chaos components however you paint them.
Out of interest why did you add green stuff to the guitar strings coming from the flame tanks? It seems weird to add a more bio feel to a model you are trying to make look like a loyalist when the component you are adding is already pretty mechanical.
What i guess i'm asking is do you intend this model to be a loyalist or traitor dread. Currently it looks like a dread recently turned to chaos yet still sporting its former chapter colours.