Below are pictures of my British MK IV helmet, his color is satin black. This helmet is in it's original condition, I have only cleaned it.
The MK IV is almost equal to the MKIII but uses a new system to hold the liner in place. It is called the "Lift Dot", this made it possible to easily remove the liner and to use the helmet shell as a bucket.
For the same reason the chin strap lugs were moved more towards the helmet rim. This way it was more stable when used as a bucket.
This helmet shell was made by RO & CO or Rubery, Owen and Company in 1952.
The liner was made by the company FFL, I haven't found any further information about this company.
See also the pictures of my MK IV helmet painted Green
Find a lot of information about the MK IV on my favorite website www.world-war-helmets.com