Visualizing contrast

When I mention " Tomorrow I will start to fix sashing in between" in the previous post I was totally wrong. 

Still I have to collect the background fabric, measure, cut and then add to the block . It's long way than tomorrow .

I spent the whole morning check the colors value whether dark, medium or light which is what the book call it  visualizing contrast .

One way is to look through red cellophane or use a reducing tool like door peephole .
Or making black and white photocopy which I did 

This is the last version of dark, medium and lights blocks of my paint box