Hoard Bronze vs Summoning Sickness

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Summoning Sickness is more saturated, cooler than Hoard Bronze.

Can I use Summoning Sickness instead of Hoard Bronze?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Summoning Sickness is more saturated, cooler than Hoard Bronze.

Can I use Hoard Bronze instead of Summoning Sickness?

The same difference applies the other way round: Hoard Bronze is more muted, 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.