Multiple Color Vector, howto in Inkscape?

So, I'm using Inkscape to convert my image to vector. It's a simple image with TWO colors. There are two distinct items in the image and one is black while the other is red, pretty simple really.

The trouble I seem to be having is when I save this image whether I save it all in one layer or I save it in two layers, doesn't seem to matter. When I upload it to Spreadshirt and I even select TWO colors at the upload screen it gets accepted okay BUT It allows me to change some invisible background color and then for the second color the entire image.

I've been looking for an answer to this the better part of all day today so here I am to ask. How do I specify in the image or wherever that ONE of the items is suppose to be black and the OTHER is suppose to be red, not both the same color. I've seen lots of other designs that do this, even allow you to change the colors yourself (such as a black letter I and a red heart).

I guess I'm missing something, and evidently it's something that's obvious to the World because I can't seem to locate the answer. Any help would be appreciated!

Thanks, in advance, for your time and assistance.

Andrew