Should colons be styled in the same way as the preceding label is?

Is it common for designers to style a colon in the same way as the preceding label, even though the following text does not follow this style?

For instance, I have the habit of making the colon bold if the label is bold as well.

Bold: the colon is bold, as is "Bold", but the text following isn't.

But when italicizing, I often do not make the colon italic (for no apparent reason, simply a habit)

Italic: the colon isn't in italics, just like the text following.

However, I think it's best to adopt an identical approach for each case. Also, in webdesign this might be crucial to provide a semantically valid HTML structure. Would one write markup like so:

<p><span class="bold">Bold:</span> the colon is bold, as is "Bold", but the text following isn't.</p>

Or like so?

<p><span class="bold">Bold</span>: the colon is not bold and neither is the text following it, but "Bold" is.</p>