Orthochromatic

Orthochromatic ("correct colors") photographic emulsion is early film emulsion, sensitive to wider range of colors than original color-blind (blue sensitive) emulsion.

Orthochromatic emulsion has too high sensitivity to blue, generally correct sensitivity to green and bright yellow, but has too low sensitivity to orange and is practically insensitive to red.

The next step in development of color sensitivity was panchromatic emulsion.