If you like gnarly insulators, this one is a winner! The surface is rough, so I'm thinking that the mold was past retirement age, but the glass is clean and without bubbles or inclusions. It's approximately a celery green color.
Caleb Thimell replied (within about 5 minutes of my posting!) that this is a CD 247.5. He notes that they come in several shades of attractive colors.
[IFONA CD 247.5]