Depending on what you want, you can try using $Translucent (gradual changes between 0% and 100% see-through-ness, but has a few rendering issues in some cases), $AlphaTest (only exactly 0% visible or 100% visible, with nothing anywhere between 0% or 100%, but mostly without rendering issues), or $Additive (only makes stuff brighter, never darker, so a black part of a texture isn't visible, while a red part of a texture would make something blue behind it appear purple instead of just overriding the blue-ness) in the material.
$Translucent and $AlphaTest require the alpha to be in the textures themselves, while $Additive just doesn't do anything when the texture is black, so alpha won't be required for $Additive.

In the context of what the screenshot shows, $Additive is probably what you'll want in this case.

Originally posted by Zappy:

Depending on what you want, you can try using $Translucent (gradual changes between 0% and 100% see-through-ness, but has a few rendering issues in some cases), $AlphaTest (only exactly 0% visible or 100% visible, with nothing anywhere between 0% or 100%, but mostly without rendering issues), or $Additive (only makes stuff brighter, never darker, so a black part of a texture isn't visible, while a red part of a texture would make something blue behind it appear purple instead of just overriding the blue-ness) in the material.
$Translucent and $AlphaTest require the alpha to be in the textures themselves, while $Additive just doesn't do anything when the texture is black, so alpha won't be required for $Additive.

In the context of what the screenshot shows, $Additive is probably what you'll want in this case.

thank you @zappy that worked perfectly!