Lens coating differences A to F to FA

I know that the design of some pentax lenses remained the same between some series (i.e A to F, F to FA) but does anyone know whether the lens coatings changed significantly between series? I ask because some of the F series lenses I have appear to have a deeper blueish/purplish coating than the FA lenses. I'm aware that the "ghostless" coating was added to some high end lens (FA Limiteds?) but I'm not sure if there were any other significant coating changes.

I would imagine that the SMC coating has been steadily developed and refined over the years. It may also change when used with different types of glass.

It does appear to be highly effective though, even with complex zoom lenses with umpteen elements.