Valkyrie Yellow vs German Yellow

How close are they?

ΔE 17.3, loose: different enough that you should pick on purpose. German Yellow is noticeably darker, more muted than Valkyrie Yellow.

Can I use German Yellow instead of Valkyrie Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). German Yellow is noticeably darker, more muted than Valkyrie Yellow.

Can I use Valkyrie Yellow instead of German Yellow?

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

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.