The purple fringing is not always axial CA. One particular sensor designer, RKM, shoots Canon and is pretty confident that cases such as this are a reflection between the microlenses and the filter stack, and should be solved by multi-coating the microlenses (rather than single AR coated, as they are now), but that's probably expensive.


[Edit] Oh yeah, and another camera designer said that purple fringing can also be caused by overload, and that disabling electronic first curtain can help. (In Canon DSLRs, electronic first curtain is controlled is the "silent mode" liveview.)