ΔE 29.4, loose: different enough that you should pick on purpose. Foul Green is a little lighter, more saturated, warmer than Ray Gun Glow.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Foul Green is a little lighter, more saturated, warmer than Ray Gun Glow.
The same difference applies the other way round: Ray Gun Glow is a little darker, more muted, 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.
See Ray Gun Glow on the colour wheel See Foul Green on the colour wheel
All matches: Ray Gun Glow equivalents · Foul Green equivalents