Sigvald Burgundy vs Dark Purple

How close are they?

ΔE 40.5, loose: different enough that you should pick on purpose. Dark Purple is noticeably darker, cooler than Sigvald Burgundy.

Can I use Dark Purple instead of Sigvald Burgundy?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 41). Dark Purple is noticeably darker, cooler than Sigvald Burgundy.

Can I use Sigvald Burgundy instead of Dark Purple?

The same difference applies the other way round: Sigvald Burgundy is noticeably lighter, 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.