Honest If I were to commission you to refurbish that I would want a blend from white at the base to light grey to light blue/gray. I would want the white to be a small portion at the base and the gray to go about 1/3 of the balance upwards and from there the blue grey to the top. For me it would be a Winter feeling although I do not know if that is acceptable by tradition and the original art deserves traditional standards.
Grimmy
First thank you for the reply. Do not take this as criticism, just trying to educate bonsai artists about scroll design...
1. I am having a difficult time understanding your terminology. I think you are explaining a Sandan Hyougu (Three step) style scroll. This is a thin strip of Ichimonji (about 1 inch or less), which borders the top and bottom of the artwork. This is the cloth I think you are advocating white with this. A chuumawashi cloth which surrounds the Ichimonji and artwork, and usually has an arabesque or other pattern in the cloth. I think you are looking for this to be your light gray cloth. Lastly the Ten and Chi is the top cloths of the scroll, and is usually a solid color with no pattern in the cloth. I think you want this to be the blue/gray color cloth.
Hopefully I interpreted that correctly.
2. This is a rule for standalone scrolls, and may not have any relevance to use of a scroll in bonsai display. It involves the concepts of use of warm and cool colors, called danshoku 暖色 and kanshoku 寒色 respectively. When a painting specifically points out a specific season, the viewer will feel that season. In the case of this painting, you can imagine feeling cold by what many others have written on it. So because of this feeling, the Hyougushi uses Danshoku (warm colors) in the cloths to help neutralize these feelings and emotions. So in this case the white and gray you suggest can both be neutral or have undertones of warm or cold depending, so that is a good choice.
3. However, another concept to think about when framing the scroll and selecting cloth colors is the painting itself. So many viewers have said it is a snowy egret...which has a lot of white. Use of white would seem to me to take away from the effect of the bird in the painting. Another thing is the age of the painting has made the paper age to almost a gray hue. Placing a gray around this old of a painting may make it look like it is not framed at all unless some techniques are utilized such as suji placed around the painting.
I will try to take some pics with cloths to try to let you visualize those points when I have more time.