I used the /give command to get a shield with damage on it,

/give JarethG100 minecraft:shield 1 179

I got a shield labeled "Black Shield", but the color of the shield was blue. When I went to repair the shield on an anvil, everytime i placed a wood plank, it would change colors until it reached full durability. The name still remains as "Black Shield". Now, after I repaired the shield, I tested its damage and found out that it also caused the shield to turn colors as its durability changed and decreased just like how it did when repairing.
There are two gifs below: Part 1 is when repairing the shield, and Part 2 is when the shield takes damage.