WiP Nurgle BSB - looking for colour advice

[strewart]

Hey all, happy to take on board any advice in general, but most significantly I am looking for suggestions on what colours to paint the Nurgle symbol (shields) on this guy's banner. As you can see I have tried a few things and not overly happy with any of them at the moment.
(I haven't finished the skulls or robe yet so I know they look flat)

 

[Terrafirma]

Rust,rust,rust , look like they have been collected over the years and you could have the rust stains dripping down the standard like a bad set of roof racks on a beach fishing truck.
put some more shading into the cloak so it doesn't just look like it's been dry brushed , put some purples or darker greens or something getting darker up into the figure .
just my two cents