ΔE 15.0, loose: different enough that you should pick on purpose. Clear Green is a little darker, more muted, cooler than Warpstone Glow. They are different kinds of paint: Citadel Warpstone Glow is an opaque base/layer paint and Reaper Clear Green is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Clear Green is a little darker, more muted, cooler than Warpstone Glow. They are different kinds of paint.
The same difference applies the other way round: Warpstone Glow is a little lighter, more saturated, 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.
See Warpstone Glow on the colour wheel See Clear Green on the colour wheel
All matches: Warpstone Glow equivalents · Clear Green equivalents