Rocket Green vs Bright Green

How close are they?

ΔE 18.3, loose: different enough that you should pick on purpose. Bright Green is noticeably lighter, more muted than Rocket Green.

Can I use Bright Green instead of Rocket Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Bright Green is noticeably lighter, more muted than Rocket Green.

Can I use Rocket Green instead of Bright Green?

The same difference applies the other way round: Rocket Green is noticeably darker, 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.