I'm trying to make a 2D animation in Blender. I created some vector graphics in Inkscape, exported it to PNG and then imported as a plane to Blender, with settings: Shadeless, Z transparent, Alpha Premultiplied. Sadly I get an image with a gray edge that is visible when images overlap

The images are perfect in Unity though:

What may cause such a problem happening? And how to get rid of it? Thanks in advance
Setting the Clip Alpha to around 0.7 made the grey edge significantly less visible, while pixelizing the image as well, but I guess it's a fair price. But it doesn't affect the red and white one when it's rendered.
– Krzysiek Jul 09 '17 at 15:43