Compare PictureBoxes

Question

Hi all,
I have 4 PictureBoxes filled with some colors. And another 4 PictureBoxes, where I write colors. And I want compare the colours of this two sets PicBoxes and the result write to another 4 PictureBoxes, that when I have the color on the same place - write black color, when I have the color on wrong place - write white color and if I have totally different color, leave the initial gray color.
I want fill colors gradually black, white, nothing...

Give me some advices or solution, please... I tried it for a long time, but unsuccesfull :-(