Sapphire's VintageColor2Strip filter simulates the old color 2-strip film process from the 1920s. The scene is exposed twice, through red and green filters, onto alternating frames of a monochrome film strip. Then the red print is dyed with a red dye, and the green print is dyed cyan. Those two strips are cemented together back-to-back to form the final print. The result contains mostly red and green colors, with some synthetic blue from the blue components of the dyes.
This effect simulates the two filter colors and the two dye colors, and also allows adding grain and color correction.