Royal Robes vs Mana Regeneration

How close are they?

ΔE 18.5, loose: different enough that you should pick on purpose. Mana Regeneration is noticeably lighter, cooler than Royal Robes.

Can I use Mana Regeneration instead of Royal Robes?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Mana Regeneration is noticeably lighter, cooler than Royal Robes.

Can I use Royal Robes instead of Mana Regeneration?

The same difference applies the other way round: Royal Robes is noticeably darker, 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.