The Ml gene (without other modifiers) doesn't change e+, eb or eWh/ey chick down. Crawford's recessive charcoal mutation didn't change wheaten chick down. There are probably multiple recessive eumelanisers.

There is one recessive black that Fred Jeffrey found in USA OEGB. This one did melanise e+ chick down, produces a purplish-black hue in the down.

I don't know if the same mutation(s) but have a look at the Brassy Back OEGB at Cackle Hatchery stock. They have Brassy back chicks in this video, say they get two different colour patterns: https://youtu.be/CH0GW7DuipQ

1 - heavily melanised smoky black chicks, remnant eye stripe, very thin remnant back stripes, head heavily melanised (looks very similar to Quail Belgian Bearded Bantams with Co). The chick legs are a bit melanised too.

2 - slightly melanised e+ chick, more smoky around wings. Central dorsal stripe melanised -smoky, not chestnut. e+ head arrow stripe slightly melanised but still visible.