Permissibility of changing gray hair with red henna mixed with black katam

Is it permissible to mix red henna with black katam and apply it to the gray hair of the beard, such that the beard appears black from a distance, but when viewed up close, the color is distinct and leans toward dark brown?
The Sunnah is to change gray hair with henna, or with henna and katam. If one changes it with henna, the color will be yellow. If one changes it with henna and katam, the color will be between red and black. There is no harm in this, and no blame, if Allah wills.