There is a small possibility that the Chiangs' are indeed color error stamp.
For those who are not familiar with the plating of this set, the entire set used one plate except the $1 value (with the denominations changed), all of the sheets can be plated. We know that due to there were studies about the broken "Hwa" variety which is found at position 19/25 on each pane of all values except the $1 value. Therefore only the $1 stamp was printed from a different plate. This provides the possibility for a color error to be made.
That said, I'm not aware of any color error stamp on this set of stamp. If they are indeed color error, there should be a handful of them exist.
As to the light/chemical treatment, yes, I have done plenty of experiments in the past. The most effective one that I found is to apply special chemical agent which is sensitive to certain spectrum light (especially ultra violet), then place the stamp under such light or about one minute, one can change the color or bleach the stamp easily. Depending on which color you want to alter, different chemical agent/light targets different color. This method was first discovered on counterfeit money. In case the color does not match the real money very well, they used this procedure to alter the shade. However, most people can't afford to buy such equipment except those try to print money themselves.
