Diplo95, you have a couple of other options:
A. You could use the same technique as mentioned here http://forums.scribus.net/index.php/topic,2314.msg10605.html#msg10605
as can be seen in the attached screenshot (top) but with a large outline (I've used 72%) and offsetting the "block" from the baseline in Advanced Settings (I've used 10%).
One issue you might have is that this technique uses outlining in a way that it's not really meant to be used and so you could have a display problem where the em dashes meet (as can be seen at the top of the blue block as a slight "square wave").
B. A lot of fonts contain "block" characters. To use these (as in the bottom screen shot):
* Double-click a text frame, then choose menu "Insert -> Glyph...".
* Press the Show Palette icon (looks like a table).
* Select Character Class "Block Elements".
* If your font has one then choose the largest.
* Then double-click it, then press the Insert button and close the dialog.
* Then copy/paste the block as many times as you want to fill the rest of the line.
You then need to alter the height/width and offset of the blocks until they're the right size for the text and frame.
Both of these techniques sound long-winded at first but once you're up and running it's easy to do and they move with the text (unlike drawing a separate box).
P.S. With both techniques just select the "blocks" and change the font colour to change the colour of the whole block.