For assist in color discrimination of color vision defects, the method of observing objects through colored filter have been known. If red filter, which absorbs mostly all light except red light, is used, only the red objects can be highly visible. In this paper, a Heilmeier type guest-host liquid crystal device with magenta dye was applied to a filter type assist device for red-green color vision defect. This device can easily control transmittance of green light by changing applied voltage, and make green objects perceived to flicker synchronously. The subjective appraisal of the assist device in color discrimination was performed by five participants with normal vision using a constructed experimental system using a video camera and a PC with a vision simulator. For the confusion indices of the Panel D-15 test, the effect of the device was statistically significant at p-value < 0.01. Moreover, a participant with color vision deficiency assessed it and got results without color confusion on the Panel D-15 test.