Cosmic Dust vs Hydromiel Yellow

How close are they?

ΔE 8.2, close: similar, with a visible difference side by side. Hydromiel Yellow is more saturated than Cosmic Dust. They are different kinds of paint: Army Painter Cosmic Dust is an opaque base/layer paint and Green Stuff World Hydromiel Yellow is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.

Can I use Hydromiel Yellow instead of Cosmic Dust?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Hydromiel Yellow is more saturated than Cosmic Dust. They are different kinds of paint.

Can I use Cosmic Dust instead of Hydromiel Yellow?

The same difference applies the other way round: Cosmic Dust is more muted.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.