I found my own answer: The trick is to have the new style "based" on an existing style that's already part of the numbering scheme.
For example, if I want to have two styles at the "Heading 2" level, one named Heading 2 and one named Heading 2 Red but both at the same level in terms of numbering, I would do the following:
- Follow the instructions linked above to set the multilevel numbering, and set it for Heading 1, Heading 2, Heading 3, etc. Leave Heading 2 Red alone, at this point.
- Edit the style for Heading 2 Red and set the "Style based on" to Heading 2. This will have it inherit the same numbering settings (and other settings) as Heading 2.
You can do this for any other styles that you want to have at the same level in your numbering scheme, e.g. a Heading 3 Red style at the Heading 3 level or another Heading 2 Green style at the Heading 2 level.
Word's TOC field can gather content for the ToC from multiple sources.
One source is "paragraphs whose styles have the Outline Levels specified by the \o parameter, so e.g.
{ TOC \o "1-2" }
Would give you a ToC with Heading 1, heading 2, and any other paragraphs whose styles have Outline Levels 1 or 2. (In other words, the current Outline Level of the paragraph is not relevant, AFAIK). In this case, a paragraph whose style has Outline Level n will appear at level n in the ToC.
You can set the Outline Level of the style by finding the style name in the style gallery in the Home tab, right-clicking, then selecting Modify... Then click the Format... dropdown at the bottom left and click Paragraph. The item you need is the "Outline Level" (which you cannot change for the built-in Heading n styles). You may not be able to modify the Outline Level if there are no paragraphs with that style in the document.
Another source is a list of specified style names using the \t parameter. This allows you to use styles that have no Outline Level. So if you want Heading 1, Heading 2, Heading 3 at ToC levels 1, 2 and 3, and "mystyle1" to be shown at ToC level 2 and "mystyle2" to be at ToC level 3, you can use
{ TOC \o "1-3" \t "mystyle1,2,mystyle2,3" }
If your Regional Settings specify ";" as the list separator character, you need to use ";" instead of "," in there.
You can also use the \t parameter to modify the ToC level where you want paragraphs with style Heading 1 etc.
These features are available from the standard ToC insertion dialog box (References->Table of Contents->Custom table of contents...->Options)
Best Answer
Of course, you can always customize the text in place.
First, select the whole line by clicking on the left margin:
Then, choose the color:
Now all the text is red! We need to change the text only back to black. Select the text from left to right, but move back a bit to exclude the "newline" character (?). Notice the difference with the one above:
Now choose "Automatic":
We're done!