Vivid Green vs Bright Green

How close are they?

ΔE 15.4, loose: different enough that you should pick on purpose. Bright Green is a little lighter, more muted, warmer than Vivid Green.

Can I use Bright Green instead of Vivid Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Bright Green is a little lighter, more muted, warmer than Vivid Green.

Can I use Vivid Green instead of Bright Green?

The same difference applies the other way round: Vivid Green is a little darker, more saturated, cooler.

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.