In your request, you specifically said you needed to retain the double border but didn't say for what purpose. If it's just for looks, the easiest way is to change the border style.
You said "The double border I was after was to be adjustable, and fillable with color." If you're just talking a little bit of adjustment, you could change the border style. Thick can be pretty darned thick, after all. But if you need to take it to extremes you probably want to Catherine did - nesting tables using padding and background. So, let's define everything above as the "guts" of the table and play with borders.
This table has a single border with a "thick" width
This table uses a single border of infinitely adjustable width (again, I picked 15 for no particular reason) and of a single color.
This table uses a double border of infinitely adjustable width (30 seemed nice this time) and of a single color. The "fill" between the lines has to stay white in this format, I think. (Someone better than me might know how to add a second color.)
This table uses the default "outset" format. The width is set in pixels and can be set as large or small as you like. I chose 15 for no special reason. I'm not sure how to make the color work in this format.
This table uses nested tables to mimic the border. The padding in the first line lets you set the thickness of the "border" and the background sets the color.
You also asked how to insert a table into another cell while retaining the border. That's essentially what I just did. The table above is a one-cell table nested inside another one-cell table. You could make that table as complicated as you need. I recommend against it, though. I prefer the control I get with a single table using colspans and rowspans.
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I think this is what you asked for. I usually design these by thinking of it as graph paper with the most discrete cell as my grid size. Then I build up, deciding which grid squares to merge into each table cell. In the case below, your most discrete cells are text 5 and 6. Everything else requires a merge of smaller cells. Rossami(talk) 08:40, 4 March 2006 (UTC)
