Why are there two legendary proficiency levels with different colors in the glory of the king?

The proficiency of heroes from low to high is white, green, blue, pink and red. The heroes just bought are all first-class white, so the second-class proficiency is green and the blue is the third-class proficiency.

Main initials: white

Middle school 100: green

Level 3 300: blue

Level 4 1000: pink

Level 5 2000: Red