Summary:
The color of the Wither's boss bar in Bedrock Edition was changed to dark purple in 1.20.40.21 Preview. This color is intentional according to MCPE-174971, so the color should also be changed in Java Edition.

Steps to Reproduce:

1. Spawn a Wither in Bedrock 1.20.40.21 and Java
2. Look at the color of the boss bar

Observed Results:
In Bedrock, the color is dark purple, while in Java, the color is a brighter purple.

Expected Results:
The color should be dark purple in both editions.

Screenshots:
Bedrock:

Java: