ΔE 26.2, loose: different enough that you should pick on purpose. Underbelly Blue is a little lighter, much more muted than Gauss Blaster Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Underbelly Blue is a little lighter, much more muted than Gauss Blaster Green.
The same difference applies the other way round: Gauss Blaster Green is a little darker, 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.
See Gauss Blaster Green on the colour wheel See Underbelly Blue on the colour wheel
All matches: Gauss Blaster Green equivalents · Underbelly Blue equivalents