White bongo discolouration

Hey all, I bought this white bongo HS with swapped black hardware from a forum member roughly 4 or 5 years ago. I bought it knowing the white would slowly cream. I love the natural cream it’s turned into. However the back of the neck is doing its own thing.

Can anyone tell me what’s going on there? The blue “rash” has been spreading and I have a few other spots where the white paint has disappeared.

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