Colors tint at shader

Hello. I am learning to write shaders. I need to check tints of input color.

 float4 frag(v2f_img i) : COLOR {
         float4 c = tex2D(_MainTex, i.uv);
     
         float cr = c.r / _Color.r;
         float cg = c.g / _Color.g;
         float cb = c.b / _Color.b;
     
         if (cr > 0.9 && cg > 0.9 && cb > 0.9) {
             //smth
         } else {
             //smth
         }
           
     }

But this code grep more then need. Apparently I do not understand something. How to grep color tint by input color with defined range?