Additional blending when using properties rather than hard-coded values for colors

TL;DR - Hard-coding a color value and using the same value via a property produces different results -- why?

I'm trying to understand shaders right now, and I've run into what seems like an anomaly while writing a CGPROGRAM. I've written the following, using a hard coded value for red:

 ...
 vertexOutput vert(vertexInput vi){
     vertexOutput vo;
     if (vi.normal.x > .9f) 
         vo.color = float4(255,0,0,255);


     vo.vertex = mul(UNITY_MATRIX_MVP, vi.vertex); 
             
     return vo;
 }            
 ...

And the results looked like this:

I then re-wrote the same code, but used a property to contain that value rather than hard code it

 ...
 Properties {
     _Color_Normal_1_0_0 ("Color_Normal_1_0_0", color) = (1.0,1.0,1.0,1.0)

     } 
 ...
 vertexOutput vert(vertexInput vi){
     vertexOutput vo;
     if (vi.normal.x > .9f) 
         vo.color = _Color_Normal_1_0_0;


     vo.vertex = mul(UNITY_MATRIX_MVP, vi.vertex); 
             
     return vo;
 }            
 ...

Using properties:

Why would the two be different if they contain the same value?