The Pythons made from 1969 to 1975 had an "E" as a prefix to the serial number. This is due to the Gun Control Act of 1968 that mandated that all firearms had to have a serial number, and the number had to be a unique number not used on any other gun.
Prior to this Colt started all models at a serial number 1.
All the "E" prefix being desirable means is that it was made earlier then later guns, and therefore the feeling is that general quality was higher.
While this may be true, you have to judge a gun on it's own merits and not just on the year it was made.
It's a little uncertain when Colt made changes in the type of grips used, since often catalogs showed older grips even though a change had been made, and often Colt used old stock until supplies were used up.
A 1975 Python would "probably" have shipped with the Third Type Colt Target grip. They would have Gold medallions, Silver being used on all other models.
Since grips were made from planks, not blocks of walnut, the grain and figure will not match, and you do see slight differences in color, but not a lot. If you see major color differences in a set of grips, it's probable one side is a replacement, especially if they don't fit well with each other.
Here's a set of Third Type Colt Target grips.
Note the checkering border under the medallions in a straight slanted line and the "thumb rests" on both sides.
Note: Medallions should be Gold, these are from a different Colt model but the actual grips were the same.
Note also that around the time of the change from the Second to Third Type there were several transition variations.
It's also possible your Python could have shipped with Second Type grips.