Gemstone vs Solar Anomalie

How close are they?

ΔE 41.7, loose: different enough that you should pick on purpose. Solar Anomalie is noticeably lighter, much more muted, cooler than Gemstone.

Can I use Solar Anomalie instead of Gemstone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 42). Solar Anomalie is noticeably lighter, much more muted, cooler than Gemstone.

Can I use Gemstone instead of Solar Anomalie?

The same difference applies the other way round: Gemstone is noticeably darker, much more saturated, 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.