Calumet sells the Roscoe Lighting Gels. They are cheap. Come in large sizes. Cut them up, put in cardboard frames, and use above the negative.
The man at aristo gaves me the values of green and blue to buy for each grade and it worked out fine.
Or use regular VC filters under the lens after the green is above the lens to cancel the excessive blue. Pull the green out only if you can`t get highh enough contrast.