This same candleholder was made by and Imperial (from Cambridge molds) and Fenton.
Rich Stoer thinks these are Cambridge in forest green even though they measure 4.5 inches which is over the 4 inches listed in Cambridge documentation.Their is documentation on his website that both the Cambridge and the Fenton candlesticks were made 4.5 inches tall.
Imperial did a 6 " tall candlestick in an irridized dark blue with the IG mark on the base.
The Fenton listing does not list a forest or emerald green color but does state that other colors were made. Many of the Fenton candleholers were marked but not al of them.
In the final analysis, the quality and clarity of the glass is the most important factor. Cambridge candleholders should have better clarity and finishing.
All measurement and color information was researched in Stoer and Felt's "The Glass Candlestick Volumes, 1,2,3"