Cosmic Dust vs Thrall Flesh

How close are they?

ΔE 22.6, loose: different enough that you should pick on purpose. Thrall Flesh is a little darker, much more muted, cooler than Cosmic Dust.

Can I use Thrall Flesh instead of Cosmic Dust?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Thrall Flesh is a little darker, much more muted, cooler than Cosmic Dust.

Can I use Cosmic Dust instead of Thrall Flesh?

The same difference applies the other way round: Cosmic Dust is a little lighter, much more saturated, warmer.

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.