Is it possible to change the default transparent color when texture painting? It seems that when exporting layers as png images in Photoshop, some elusive semi-transparent pixels may be saved as white and become quite apparent when imported as planes into blender. 



This could be easily remedied by erasing their alpha in the texture paint mode; however, transparent becomes white: 



This makes it very hard in most, and impossible in some, cases to tell where these stray pixels are and when I've gotten rid of them ("erasing alpha" is basically painting "white" over white).

Any way to get rid of the transparent white by either replacing it with a different colour, hiding it completely or replacing it by some Photoshop-style grid?
In your material settings for your image texture - the material in the Shading tab of the properties panel needs to have Z Transparency turned on for the GLSL viewport to allow you to 'see' the erase alpha as the background showing through.