Post list of list of model object to Controller in ASP.NET MVC

Your generating inputs with name attributes that have no relationship to your model, therefore cannot be bound by the DefaultModelBinder. You need to start by generating the data in the controller (not in the view) so that you can bind to your model.

The following assumes you change your SizeColorQuantities property to List<SizeColorQuantityViewModel>

public ActionResult Create()
{
    var colors = new List<string>(){ "Red", "Blue" };
    var sizes = new List<string>(){ "S", "M", "L", "XL" };

    var model = new ProductViewModel()
    {
        Product = "My product",
        SizeColorQuantities = new List<SizeColorQuantityViewModel>
    };
    foreach(var color in colors)
    {
        var child = new SizeColorQuantityViewModel()
        {
            ColorId = color,
            SizeAndQuantities = new List<SizeAndQuantity>
        };
        model.SizeColorQuantities.Add(child);
        foreach(var size in sizes)
        {
            child.SizeAndQuantities.Add(new SizeAndQuantity()
            {
                SizeId = size // assumes SizeId is changed to string, not int
            });
        }
    }
    return View(model);
}

You now have a correctly populated view model that will be passed to the view which you can bind to with strongly typed HtmlHelpers inside nested for loops

@model ProductViewModel
....
@using (Html.BeginForm())
{
    ....
    @for(int i = 0; i < Model.SizeColorQuantities.Count; i++)
    {
        @Html.TextBoxFor(m => m.SizeColorQuantities[i].ColorId, new { @class = "form-control", @readonly = "readonly" })
        for (int j = 0; j < Model.SizeColorQuantities[i].SizeAndQuantities .Count; j++)
        {
            @Html.TextBoxFor(m => m.SizeColorQuantities[i].SizeAndQuantities[j].SizeId, new { @class = "form-control", @readonly = "readonly" })
            @Html.TextBoxFor(m => m.SizeColorQuantities[i].SizeAndQuantities[j].Quantity, new { @class = "form-control" })
        }
    }
    <input type="submit" ... />
}

Note: Always use the strongly typed ***For() HtmlHelper methods and never attempt to set the value (or name) attribute when using a HtmlHelper method.

Your POST method now needs to be

[HttpPost]
public ActionResult Create(ProductViewModel model)
{
    ....
}

Note you can also use custom EditorTemplate's for your types as explained in HTML Table to ADO.NET DataTable, which also explains how your name attributes must be generated in order to bind to collections. In your case, for example your Quantity inputs need to be (compare that to what your currently generating)

<input name="SizeColorQuantities[0].SizeAndQuantities[0].Quantity" ... />
<input name="SizeColorQuantities[0].SizeAndQuantities[1].Quantity" ... />
....
<input name="SizeColorQuantities[1].SizeAndQuantities[0].Quantity" ... />
<input name="SizeColorQuantities[1].SizeAndQuantities[1].Quantity" ... />
....