It becomes hard to see the checked checkboxes because of the selected color it has by default matches the select color of the grid

Solution:

        .RadGrid_BlackMetroTouch .rgSelectedRow .RadCheckBox.RadButton_BlackMetroTouch .rbToggleCheckboxChecked::before,
        .RadGrid_Bootstrap .rgSelectedRow .RadCheckBox.RadButton_Bootstrap .rbToggleCheckboxChecked::before,
        .RadGrid_Metro .rgSelectedRow .RadCheckBox.RadButton_Metro .rbToggleCheckboxChecked::before,
        .RadGrid_MetroTouch .rgSelectedRow .RadCheckBox.RadButton_MetroTouch .rbToggleCheckboxChecked::before {
            color: white;
        }

        .RadGrid_Glow .rgSelectedRow .RadCheckBox.RadButton_Glow .rbToggleCheckboxChecked::before,
        .RadGrid_Office2010Black .rgSelectedRow .RadCheckBox.RadButton_Office2010Black .rbToggleCheckboxChecked::before,
        .RadGrid_Telerik .rgSelectedRow .RadCheckBox.RadButton_Telerik .rbToggleCheckboxChecked::before,
        .RadGrid_WebBlue .rgSelectedRow .RadCheckBox.RadButton_WebBlue .rbToggleCheckboxChecked::before {
            color: black;
        }

Sample to reproduce the behavior and compare the default colors in other states/cases:

        <telerik:RadCheckBox runat="server" ID="rcb1"></telerik:RadCheckBox>
        <br />
        <telerik:RadCheckBox runat="server" ID="rcb2" Checked="true"></telerik:RadCheckBox>
        <telerik:RadSkinManager runat="server" ID="RadSkinManager1" Skin="Bootstrap" ShowChooser="true">
        </telerik:RadSkinManager>
        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" RenderMode="Lightweight" />
        <asp:CheckBox ID="Checkbox1" Text="some checkbox" runat="server" />
        <telerik:RadGrid ID="RadGrid1" runat="server" OnNeedDataSource="RadGrid1_NeedDataSource" RenderMode="Lightweight">
            <MasterTableView>
                <Columns>
                    <telerik:GridClientSelectColumn></telerik:GridClientSelectColumn>
                    <telerik:GridTemplateColumn HeaderText="rad check box column">
                        <ItemTemplate>
                            <telerik:RadCheckBox runat="server" ID="RadCheckBox1"></telerik:RadCheckBox>
                            <br />
                            <telerik:RadCheckBox runat="server" ID="RadCheckBox2" Checked="true"></telerik:RadCheckBox>
                        </ItemTemplate>
                    </telerik:GridTemplateColumn>
                </Columns>
            </MasterTableView>
            <ClientSettings>
                <Selecting AllowRowSelect="true" />
            </ClientSettings>
        </telerik:RadGrid>

And a dummy data source that is not a good data source in general, but it will suffice to get this running so one can observe

    protected void RadGrid1_NeedDataSource(object sender, GridNeedDataSourceEventArgs e)
    {
        (sender as RadGrid).DataSource = "abcdef";
    }