227 Transparent Bright Yellowish Green / Trans-Bright Green
BrickLink: Trans-Bright Green (includes other colors too)
Introduced in Belville and Clikits in 2003. Last used in 2006, I believe, this color was never used outside those two themes and Duplo.
Oddly, the Clikits parts glow faintly under a blacklight, while the Belville ones do not glow at all. BrickSet tells us Lego considered them the same color.