Transparent Black vs Ink Sepia

How close are they?

ΔE 9.4, close: similar, with a visible difference side by side. Ink Sepia is a little lighter, more saturated than Transparent Black.

Can I use Ink Sepia instead of Transparent Black?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Ink Sepia is a little lighter, more saturated than Transparent Black.

Can I use Transparent Black instead of Ink Sepia?

The same difference applies the other way round: Transparent Black is a little darker, 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.