3D effect - blending sprites

Hi, I am making a game where two pictures: blue and red are moving away from each other to see how long one can see the 3D effect. My problem is that the sprites don't blend with each other and there's no 3D effect at all, instead one of them is overlapping the other one. I was trying to decrease the alpha variable, but stil one of the pictures is too dominant.
I guess that the answer is either to blend them or use some shader, but, as I've never worked with anything like this, it seems quite complicated.
Is there an easy way to blend the pictures? Or another simple way this could be done?