Character behind obstacles shader, multiple Pass issue

Hi,

I'm starting my adventure with shaders, and having limited knowledge I don't know where else to look for the solution. My goal was to have a simple shader that renders an object just with color, but if the object is hidden behind other objects, use another color (so that a character position is known even if behind an obstacle). This is what I wrote:

 Shader "Custom/TestShader"
 {
     Properties 
     {
         _Color1 ("Color1", Color) = (1,1,1,1)
         _Color2 ("Color2", Color) = (1,1,1,1)
     }
     SubShader 
     {
         Tags { "Queue" = "Overlay" }
         
         Pass 
         { 
              ZWrite Off
              ZTest Greater
              Lighting Off
              Color [_Color1]
         }
         Pass 
         {
             ZTest Less      
             Color [_Color2]
         }
     }
 }
 

The problem is that the only first Pass block seems to be working. If I switch the Pass blocks order, still only the first one seems to be working but the other one is not. Here's whats happening with Pass blocks in different order:

I'm using URP. Can someone point me to the right direction with this? Why is only the first block working? Is there something obvious I'm missing?