For an imaginary table eight columns wide, here is my code:

<colgroup>
<col />
<col />
<col span="3" />
<col span="3" style="background-color: red;" />
</colgroup>

Expected result: Columns 6, 7, and 8 are red
Result in browser: Columns 6, 7, and 8 are red (Tested in Safari, Chrome, Firefox)
Prince result: Column 3 is red

I'm using prince via Docraptor and haven't had a chance to test in current prince in command line.

The span attribute is not supported in Prince at this time.