The Bug

If you're writing an advancement description with JSON, the description will ignore your first specified color, no matter if it's a word or a hex value, and use the default color instead. This is different to how it used to work.

The Workaround

Instead of writing

{"text":"Kill three unique mobs with one piercing crossbow shot","color":"white"}

write this

["",{"text":"Kill three unique mobs with one piercing crossbow shot","color":"white"}]