greyscale slider in Designer as brush opacity in Painter ( for changing colors)

Hi everyone. 

Could you help me please? 
As in title.
I had an idea to create simple material with disolve, blur and blends. It  works by slider in Designer and also in Painter but I have no idea how to export it to Painter to make it work as opacity value (by brush opacity 0- red then blend to green 0.1 to 0,5 value and blend to blue 0.59- 1.0 ) . 

In short words. I would like to make a material where color will change depends by brush opacity in Painter.  Is it possible? I guess my idea was completely wrong? Maybe there is any simplier way to do what I would like to. 

Thanks for any help.  🙂