It appears this bug was marked as “Won’t Fix”. Why? It is not limited to when using color picker in animations, it’s happening to me even in the UMG designer on 4.25.
This issue is marked as a “Won’t fix”, but it is not reproduced and has already been fixed in 5.0. If you want to apply the fix to UE4.25, I hope the following pull-request will help. This request is currently in reviewing, but this change is limited and may not be merged.