Tienes que poner la propiedad ownerdraw a true y en el evento ondrawTab un codigo como este
Código Delphi
[-]
procedure TForm.PageControlDrawTab(Control: TCustomTabControl;
TabIndex: Integer; const Rect: TRect; Active: Boolean);
var
AText: string;
APoint: TPoint;
begin
with (Control as TPageControl).Canvas do
begin
if(active) then
begin
Brush.Color := rojo;
end
else
begin
Brush.Color := verde;
end;
FillRect(Rect);
AText := TPageControl(Control).Pages[TabIndex].Caption;
with Control.Canvas do
begin
APoint.x := (Rect.Right - Rect.Left) div 2 - TextWidth(AText) div 2;
APoint.y := (Rect.Bottom - Rect.Top) div 2 - TextHeight(AText) div 2;
TextRect(Rect, Rect.Left + APoint.x, Rect.Top + APoint.y, AText);
end;
end;
end;