Mana Regeneration vs Mystic Blue

How close are they?

ΔE 28.5, loose: different enough that you should pick on purpose. Mystic Blue is noticeably darker, more muted, warmer than Mana Regeneration.

Can I use Mystic Blue instead of Mana Regeneration?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Mystic Blue is noticeably darker, more muted, warmer than Mana Regeneration.

Can I use Mana Regeneration instead of Mystic Blue?

The same difference applies the other way round: Mana Regeneration is noticeably lighter, more saturated, 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.