Bright Gold vs Tropical Green

How close are they?

ΔE 28.8, loose: different enough that you should pick on purpose. Tropical Green is a little lighter, more saturated, cooler than Bright Gold.

Can I use Tropical Green instead of Bright Gold?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Tropical Green is a little lighter, more saturated, cooler than Bright Gold.

Can I use Bright Gold instead of Tropical Green?

The same difference applies the other way round: Bright Gold is a little darker, 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.