Will chocolate dials stop altering?

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Blue dials from that era are notoriously unstable and ultimately lose color completely. I don't think you can extrapolate to a brown Speedmaster dial.
 
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I’d agree both are unstable but due to different factors and thus have different modes and rates of deterioration.
Blue dials for example often lose their finish entirely around the lume plots and fade to an unattractive grey hue.