Dark Magenta vs Wyvern Fury

How close are they?

ΔE 19.4, loose: different enough that you should pick on purpose. Wyvern Fury is a little lighter, more muted, warmer than Dark Magenta.

Can I use Wyvern Fury instead of Dark Magenta?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Wyvern Fury is a little lighter, more muted, warmer than Dark Magenta.

Can I use Dark Magenta instead of Wyvern Fury?

The same difference applies the other way round: Dark Magenta is a little darker, 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.