Parker case colors
 

How did the original case colors vary across the grades of the same period? Put another way, are the case colors of a 1904 CHE the same to a VHE of the same year?

Similar would be the word I use to compare. I would imagine the same process was used no matter the grade, the results would vary but would have resulted in similar colors. Just my thoughts on the matter.

I believe the actual case colors didn't change from grade to grade and from the early years to later years however the placement of the colors did. In the early years each color blended in to the other where in later years the colors were more spotty, if that is the correct term. JMO.

There was no variation at all in the process for the grades of gun. So the effects will not be any different except for the normal variation from gun to gun.

Now, the appearance can look a bit different due to increased amounts of engraving. Meaning that colors and patterns may not look as clear or vivid. But usually one will not see a major change in appearance until you get into the grades with more full coverage engraving and deeper engraving.

The SC trap guns with all the stippling on them are a perfect example of a surface that can hide a lot of case color.

With regard to Brian's comment, Engraving has a great effect on the appearance of case hardening colors. When the gun is new, the light is reflected erratically and as the gun gets used, all the 'high spot's' colors on the edges adjacent to the graver's cut, wear more quickly, leaving only the colors in the depth of the graver's cut.

Significant amount of original case colors here