There are two parts - how to get similar hashes for similar versions and how to display hash as a color line.
Displaying hash it as a color line should be simple, every digit in hash can be mapped to color palette, and the result will be line of colors corresponding to the hash value.
Getting similar caches is more complex, I know two methods how to do it.
It's simple and robust approach with good quality but the limitation is - it only can compare single origin version with others, it can't compare two arbitrary versions. But maybe we still can use it - use latest version as origin and show how previous are different from it.