You need to force the style for newly added elements:
procedure TForm1.FormCreate(Sender: TObject);
var
itTab: TTMSFMXTile;
shp: TTMSFMXTileShape;
begin
itTab := TMSFMXTileList1.Tiles.Add();
itTab.Caption := 'caption';
itTab.Notes := 'notes';
TMSFMXTileList1.NeedStyleLookup;
TMSFMXTileList1.ApplyStyleLookup;
shp := itTab.Shape;
if Assigned(shp) then
shp.Fill.Color := claGreen;
end;
But the best approach would be to set the color via the OnCustomizeTile:
procedure TForm1.FormCreate(Sender: TObject);
var
itTab: TTMSFMXTile;
begin
itTab := TMSFMXTileList1.Tiles.Add();
itTab.Caption := 'caption';
itTab.Notes := 'notes';
end;
procedure TForm1.TMSFMXTileList1CustomizeTile(Sender: TObject;
ATile: TTMSFMXTile; ATileShape: TControl);
begin
ATile.Shape.Fill.Color := claGreen;
end;