How about hanging a perpetual calendar with a green font in the Feng Shui room?

Yes, hanging a perpetual calendar is not about color, but about personal preference.

Generally, a digital perpetual calendar for home use or a lucky digital perpetual calendar can be hung on the wall opposite the door. Therefore, a digital calendar with no specific meaning can be hung on the opposite side of the door. But some digital calendars can't be hung in the opposite place, such as Christian digital calendars or digital calendars with pictures of other sects. Wan Nianzhong can be hung on the left (Qinglong) side of the living room, because the Qinglong side is auspicious. It can be hung in front (Suzaku), and the clock in front can be moved, so it can be hung in front. Calendars can't be placed on the right side of the living room (white tiger), because white tigers are fierce and easy to move. Nor can it be placed behind the living room (Xuanwu), because Xuanwu should be quiet and motionless.