Ok work done in 4 min!!!!!

I pick up the ground color and the desire shadow color from the image put the value in the Lit Color and Shadow Color set the Calibrate value to Zero and render my color shadow with one simple light.. for the extra  blending color tones set the Shadow Blur Radious to 20 in some cases and it work briliant.. THANK YOU BB!!!!!! it can't be more simple... ...and render so much faster as the shadow catcher feature...

i did not used it with a good light so just for simple quick  test ...

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"Surrender to what it is - Let go of what was - Have faith in what will be "