By default, when you create new table, it has the folowing properties.

width - 320 px
border color - #000000
border width - 1
border style - solid
rows - 3
columns - 4

You can change these default properties (and some others).

Example

<ed:Editor id="editor" runat="server">
    <DefaultTable Rows="2" Columns="5" BorderStyle="Dotted" BorderColor="#0000FF" />
</ed:Editor>

You will get the following result



See HTML Editor inner properties page for details.