Red does have an accounting purpose.  Any negative figures are shown in red.  The red underscore can be used for emphasising something - for instance when typing an address, For the Attention of : F. Bloggs  There are many other examples, these are just a few.  And finally, if you fit an all-black ribbon, by leaving the setting on red, you can use up the bottom half of the ribbon once you have used up the ink on the top.  Early Royal flat bed typewriters had the ribbon control marked 'Upper' and 'Lower', not 'Black' and 'Red' implying that this was the real purpose of the ribbon control.

Underwood09 wrote:

Thanks for the reply, I'm a traditionalist, so will likley keep using the red/black as Underwood intended. Much like keeping my vintage MGB a four cylinder four speed, despite pressure to install a Rover V-8 and five speed, or even (Gasp) a Miata drive line. Regarding the bichrome, I've also seen them in green/black. I'll assume it's much the same thing as the multiple color options offered for the IBM Selectrics back in the day. 

Thanks for keeping your MGB original and honoring the original designers! Vive la History!

Regarding the bichrome, ribbons are currently available in a wide variety of color combinations, but I'm confused by your reference to "multiple color options offered for the IBM Selectrics". Selectrics never had bichrome ribbons and to change colors you changed out the whole cartridge. This is nothing at all like bichrome ribbons. Or do you mean something else?