Inktense Cyan vs Smoke Ink

How close are they?

ΔE 39.3, loose: different enough that you should pick on purpose. Smoke Ink is a little darker, much more muted than Inktense Cyan.

Can I use Smoke Ink instead of Inktense Cyan?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 39). Smoke Ink is a little darker, much more muted than Inktense Cyan.

Can I use Inktense Cyan instead of Smoke Ink?

The same difference applies the other way round: Inktense Cyan 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.