Transparent Brown vs Ink Sepia

How close are they?

ΔE 22.3, loose: different enough that you should pick on purpose. Ink Sepia is a little darker, much more muted than Transparent Brown.

Can I use Ink Sepia instead of Transparent Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Ink Sepia is a little darker, much more muted than Transparent Brown.

Can I use Transparent Brown instead of Ink Sepia?

The same difference applies the other way round: Transparent Brown is a little lighter, much more saturated.

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.