A variation of Darkfield Illumination was invented by Julius Rheinberg in 1896, and is called Rheinberg Illumination. It uses colored filters in place of the DF stop.
Rheinberg illumination uses a Color Darkfield Stop to illuminate the sample with two different colors of light. The central area, where the DF stop would be, is one color (e.g., green) and the outer ring (annulus) a contrasting color (e.g., red). Unmodified light (light that does not impinge on the sample) fills the background with uniform light the color of the central circle. Modified light (light that impinges on the sample and is refracted) is the color of the outer annulus. In this example, the sample would be red on a green background.

Rheinberg stops can be almost any color combination.

You can make your own Rheinberg color stop using a color laser printer and transparency film. The stop will be the diameter of the condenser filter holder. The diameter of the central circle will be the diameter of the field of view for any given objective. Adjust the condenser for Köhler illumination, remove an eyepiece, open the Condenser Iris until it just fills the objective (seen through the eyepiece tube), measure the diameter of the condenser aperture.