When doing two passes on different alphas, shader gets overwritten.

When I do two passes and apply either a red or green texture to the pixel depending on if the alpha is over or under 0.5 using SetTexture, I get a shader in full red or full green, but not half-red/half-green, even though half of the texture is under 0.5 alpha and the other half is over 0.5 alpha. Here is my code:

  Shader "Examples/Self-Illumination 3" {
         Properties {
             _MainTex ("Main texture", 2D) = ""
             _Red ("Red texture", 2D) = ""
             _Green ("Green Texture", 2D) = ""
             
         }
     
         SubShader {
         
             Pass {
                 AlphaTest GEqual 0.5
                 Lighting On
                 SetTexture [_Red] {
                 }
             }
             Pass {
                 AlphaTest Less 0.5
                 Lighting On
                 SetTexture [_Green] {
                 }
             }
         }
     }

PS In my second pass, when I set the texture back to my main texture, I get half red and half of my main texture, so it works. However, I want it to be half red and half green.