if you Alpha blend
a pre-multiplied
texture the darks get darker like that - alpha blend multiplies the texture by inverse of alpha
either
-
make the RGB just plain white
Alpha == your dot shape because alpha blending is {Source x (1-alpha)
} -
or change blend mode on your master node to pre-multiplied alpha {
Source x One
}
this will mean to make your dot vanish you must lower alpha AND color to black to make it vanish, but you get the benefit of being able to make it additive too