Summoning Sickness vs Greenish Gold

How close are they?

ΔE 15.3, loose: different enough that you should pick on purpose. Greenish Gold is a little darker, much more muted than Summoning Sickness.

Can I use Greenish Gold instead of Summoning Sickness?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Greenish Gold is a little darker, much more muted than Summoning Sickness.

Can I use Summoning Sickness instead of Greenish Gold?

The same difference applies the other way round: Summoning Sickness is a little lighter, much 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.