Transparent Fluorescent Green
From Brickipedia, the LEGO Wiki
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| Transparent Fluorescent Green Colour-ID: 49 (Colour palette) | 
Transparent Fluorescent Green (Colour-ID: 49), colloquially known as neon green, is a colour for transparent LEGO elements. The first parts molded in this colour were introduced in 1990 as part of the LEGO Space sub-theme M-Tron. The colour is still in use today.
It should be noted that this colour is actually yellow chartreuse.
 
						 
