calculate alpha value backwards

Hi guys,

I've got a question. I've got the color values for the rgb mode (7/54/100). I also know that this color is generated by an alpha value of 89 percent. Is it possible to calculate the origin value of the color backwards. I want to know which color is needed to get the color (7/54/100) with an alpha value of 89%. The background is white (255/255/255). Is their any possibility for this calculation. Thank you very much indeed for your replies.

Kai,

Your incomplete question is unanswerable. Just citing the resultant RGB values is giving insufficient data for determining underlying alpha values, which depend on RGB values of layer and substrate AND which of over twenty blend modes has been invoked.