So, after a bit of experimentation, there seems to be something unusual about the alpha in your image. Currently, when I open your file and press f5, I get the washed out version like you. When I recreated and output a heart image like yours from Inkscape though, and replaced yours with it, … it works fine.
You can even see the difference in alpha in Blender’s texture selector dropdown (yours is up the top, mine down the bottom):
In short, I suspect this isn’t actually an Armory issue per se, so much as a Blender one, as our png images show up differently in Blender even before Armory is started.
I’m wondering if this is some kind of premultiplied alpha issue or similar…