Dark Blue Tone vs Tyran Blue

How close are they?

ΔE 40.1, loose: different enough that you should pick on purpose. Tyran Blue is noticeably lighter, much more saturated, cooler than Dark Blue Tone.

Can I use Tyran Blue instead of Dark Blue Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 40). Tyran Blue is noticeably lighter, much more saturated, cooler than Dark Blue Tone.

Can I use Dark Blue Tone instead of Tyran Blue?

The same difference applies the other way round: Dark Blue 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.