Following problem: I have two textures and I want to combine these two into a new texture. Thus, one texture is used as background, the other will be overlaid. The overlay texture is getting initialized with glClearColor(1.0, 1.0, 1.0, 0.0). Objects are draw onto the texture, these objects do have alpha values.

Now blending between the two textures leaves a white border around the objects. The border comes from the fact that the background color in the second texture is white, isn't it?

How can I use alpha blending where I do not have to think about the background color of the overlaying texture?