ΔE 18.8, loose: different enough that you should pick on purpose. Solar Sand is noticeably lighter than Gehenna's Gold.
Can I use Solar Sand instead of Gehenna's Gold?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Solar Sand is noticeably lighter than Gehenna's Gold.
Can I use Gehenna's Gold instead of Solar Sand?
The same difference applies the other way round: Gehenna's Gold is noticeably darker.
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.