How to differentiate between similarly coloured faces

why don’t you select the tops of the stairs, and make them diffrent material? i don’t know much about cad, but in blender you can select the vertecies you want and add them to a new material

EDIT: Shader and Pictures

Above you see my implemention of a Quadbased Wireframe Shader and a Triangle Wireframe shader

The Code is this:

 Shader "GeometryShading/Wireframe"
 {
     Properties
     {
         [HideInInspector]_MainTex("MainTex", 2D) = "black" {}
         _WireSmoothness("Wireframe Smoothness", RANGE(0, 400)) = 400
         _WireThickness("Wireframe Thickness", RANGE(0, 10)) = 10
         _WireColor("Wireframe Color", color) = (1,1,1,1)
         _Color("Main Color", Color) = (1,1,1,1)
         [Toggle] _RemoveDiag("Remove diagonals?", Float) = 0.
     }
         SubShader
         {
             Tags{ "Queue" = "Geometry" "RenderType" = "Opaque" }
 
             //Simple Color Base Shader
 
             Pass
             {
 
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"
 
 
             float4 _Color;
 
             struct v2f
             {
                 half3 worldNormal : TEXCOORD0;
                 float4 pos : SV_POSITION;
             };
 
             v2f vert(float4 vertex : POSITION, float3 normal : NORMAL)
             {
                 v2f o;
                 o.pos = UnityObjectToClipPos(vertex);
                 o.worldNormal = UnityObjectToWorldNormal(normal);
                 return o;
             }
 
             fixed4 frag(v2f i) : SV_Target
             {
                 fixed4 c = 0;
                 c.rgb = _Color;
                 return c;
             }
             ENDCG
         }
 
 
         //Wireframed Shader with Option to disable Diagonals
             Pass
             {
             Cull Back
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma geometry geom
             #pragma shader_feature __ _REMOVEDIAG_ON
             #include "UnityCG.cginc"
 
             float _WireSmoothness;
             fixed4 _WireColor;
             float4 _Color;
             uniform float _WireThickness;
             uniform sampler2D _MainTex; uniform float4 _MainTex_ST;
 
         struct appdata
         {
             float4 vertex : POSITION;
             float2 texcoord0 : TEXCOORD0;
             UNITY_VERTEX_INPUT_INSTANCE_ID
         };
         struct v2g
         {
             float4 worldPos : SV_POSITION;
             float2 uv0 : TEXCOORD0;
             UNITY_VERTEX_OUTPUT_STEREO
         };
 
         struct g2f
         {
             float4 pos : SV_POSITION;
             float4 bary : TEXCOORD0;
             UNITY_VERTEX_OUTPUT_STEREO
         };
 
         v2g vert(appdata v)
         {
             v2g o;
             UNITY_SETUP_INSTANCE_ID(v);
             UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
             o.worldPos = mul(unity_ObjectToWorld, v.vertex);
             o.uv0 = TRANSFORM_TEX(v.texcoord0, _MainTex);
             return o;
         }
 
         [maxvertexcount(3)]
         void geom(triangle v2g IN[3], inout TriangleStream<g2f> triStream) {
         float3 param = float3(0., 0., 0.);
         float wireThickness = 13 - _WireThickness;
 
         #if _REMOVEDIAG_ON
             float EdgeA = length(IN[0].worldPos - IN[1].worldPos);
             float EdgeB = length(IN[1].worldPos - IN[2].worldPos);
             float EdgeC = length(IN[2].worldPos - IN[0].worldPos);
 
             if (EdgeA > EdgeB && EdgeA > EdgeC)            { param.y = 1.;}
             else if (EdgeB > EdgeC && EdgeB > EdgeA)    { param.x = 1.;}
             else                                        { param.z = 1.;}
         #endif
 
             g2f o;
 
             o.pos = mul(UNITY_MATRIX_VP, IN[0].worldPos);
             o.bary.xyz = (float3(1., 0., 0.) + param) * o.pos.w * wireThickness;
             o.bary.w = 1 / o.pos.w;
             UNITY_TRANSFER_VERTEX_OUTPUT_STEREO(i[0], o);
             triStream.Append(o);
 
             o.pos = mul(UNITY_MATRIX_VP, IN[1].worldPos);
             o.bary.xyz = (float3(0., 0., 1.) + param) * o.pos.w * wireThickness;
             o.bary.w = 1 / o.pos.w;
             UNITY_TRANSFER_VERTEX_OUTPUT_STEREO(i[1], o);
             triStream.Append(o);
 
             o.pos = mul(UNITY_MATRIX_VP, IN[2].worldPos);
             o.bary.xyz = (float3(0., 1., 0.) + param) * o.pos.w * wireThickness;
             o.bary.w = 1 / o.pos.w;
             UNITY_TRANSFER_VERTEX_OUTPUT_STEREO(i[2], o);
             triStream.Append(o);
         }
 
         fixed4 frag(g2f i) : SV_Target
         {
 
             if (!any(bool3(i.bary.x <= 0.5, i.bary.y <= 0.5, i.bary.z <= 0.5)))
             {
                 discard;
             }
             
             float minDistanceToEdge = min(i.bary[0], min(i.bary[1], i.bary[2])) * i.bary[3];
             float4 basecol = tex2D(_MainTex, i.bary);
             if (minDistanceToEdge > 0.9)
             {
                 return fixed4(basecol.rgb, 0);
             }
             float t = exp2(_WireSmoothness * -1.0 * minDistanceToEdge * minDistanceToEdge);
             fixed4 finalcolor = lerp(_Color, _WireColor, t);
             return finalcolor;
         }
 
             ENDCG
         }
     }
 }

if you have further questions, just ask