Troglodyte Blue vs Meredius Blue

How close are they?

ΔE 27.9, loose: different enough that you should pick on purpose. Meredius Blue is noticeably lighter, warmer than Troglodyte Blue.

Can I use Meredius Blue instead of Troglodyte Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Meredius Blue is noticeably lighter, warmer than Troglodyte Blue.

Can I use Troglodyte Blue instead of Meredius Blue?

The same difference applies the other way round: Troglodyte Blue is noticeably darker, cooler.

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.