Strong Tone vs Ancient Sepia

How close are they?

ΔE 50.4, loose: different enough that you should pick on purpose. Ancient Sepia is noticeably lighter, much more saturated, cooler than Strong Tone.

Can I use Ancient Sepia instead of Strong Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 50). Ancient Sepia is noticeably lighter, much more saturated, cooler than Strong Tone.

Can I use Strong Tone instead of Ancient Sepia?

The same difference applies the other way round: Strong Tone is noticeably darker, much more muted, 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.