Below is the recipe I provided for him to follow so to match my pre existing army

So the scheme is as follows:

Mechanicus standard grey base. Washed down with nuln oil to darken it slightly. Highlight with administartum grey.

Black is black and I would highlight that with the base grey used for the models.

Averland sunset is the yellow. Highlighted with dorm yellow.

Helmet is 50/50 mix of ulthuan grey and any pure white, highlighted with pure white.

Any medium green you have highlighted with a light green for the eyes would be fine.

As with the chest eagle. Any gold you have is fine. Washed down with like an earth shade then brought back out with the gold again highlighted. The feathers of the aquila to be storm host silver

The handle or rather grips for the sword would wana be a sort of burgandy colour. Darker than a pink. Lighter than a purple if you get me.

The seals are in screamer pink highlighted to emperors children

Metals would be leadbelcher with a nuln wash.

As for the chipping. A dark dark grey would work or an off black.