The specular value of the Principled BSDF Node was exported as a greenish color which was shown like that in some rendering engines by default.
I changed it so that the specular level is applied as a greyscale color with alpha fixed to 1.
thanks for the patch. I took a look at this and i found that actually the shader value is not a color but a factor, so the function returns completely wrong data. So actually Collada should not export a specular color but a specular factor. I will add a fix for this.