I'm having my 66 F100 240 ci engine steam cleaned and then I want to paint it the original block color. The motor is so dirty and showing no paint color. I'm wondering what was the stock engine color?

 

most likely black, but don't quote me on that, my 65 352 is black

 

I believe in 66 they were ford blue.even the valve cover.

 

It would be the lighter ford blue if it was a blue at all. The darker didn't come out until the mid or late 70's. There is also a ford red and green that may have been used. You will find the original color somewhere around the mounts if not under them or on the back of the block.