Hello,
I have a suggession for TPagecontrol class. It has "onChange" and "onChanging" property. onChange trigger after changED, Its okey, I wish name can be "onChanged" okey never mind. My suggestion is, new event or change "onChange" events property.

My suggestion notify event is on TPageControl class or on TCustomTabControl class :
TonChanged = procedure(Sender: TObject; aCanvas : TCanvas) of object;

Sender is TTabSheet so I can get info, Pageindex, caption etc. aCanvas for change font's info size, name, color etc. and background color change (Canvas.Bursh.Color) so I can signalize selected tabsheet.

or this can be OnOwnerDraw event, so colored each tabsheed , Programmer write small code for activepage, or what they want, for exaple if tab's caption is long, shorten caption and add "..." etc.

On IDE's component palet, if selected tab font's be bold and blue color, its good view :)
Thank you