Stage3D - Semi transparent Textures

OK, here’s another Stage3D question.

I’ve got layered textures in one scene with one object having a texture of a semi transparent white colour. When rendered in the scene, it does appear to be semi transparent but instead of white it’s coming up as a dull grey colour.

I have read elsewhere that it could be something to do with pre-multiplied alphas and that you can use BlendMode.ADD to solve this when capturing the bitmapdata to upload to the texture but I’m unable to get this to work.

Anyone come accross this issue before and know a solution?