Using Delphi XE7 on a Windows 7 Pro 64-bit system. If I choose \'Charcoal Dark Slate\' VCL style, the 16x16 pixel titel bar icon down-sized from the 32x32 program icon looks
This is known issue with VCL Styles http://qc.embarcadero.com/wc/qcmain.aspx?d=106224
Also see this issue in Embarcadero's newer QC site: https://quality.embarcadero.com/browse/RSP-11572 --- it's been 3 years since initially reported, and still not fixed. If enough people vote for that issue, maybe it will get some attention.
As workaround you can load proper 16x16 icon into form's Icon property.
In order for that to work you have to also set Application.MainFormOnTaskBar := false; in your .dpr file
However that has some other undesirable effects because it will disable Windows Vista or Windows 7 Aero effects, including live taskbar thumbnails, Dynamic Windows, Windows Flip, and Windows Flip 3D. See: MainFormOnTaskBar
In any case do not change your application icon size because it is the worst solution.