Shader syntax woe ... !

Shader “CTD/SimpleDiffuse”
{
Properties
(
_ColorTint(“Color Tint”, Color) = (1,1,1,1)
}

SubShader
(
    Tags ( " RenderType"-"Opaque" )
    
    CGRPROGRAM
    #Pragma surface surf lambert
    
    struct input
    {
       float color : COLOR;
    };
    
    void surf (Input IN, input SurfaceOutput o)
    {
        o.Aidedo - IN.color;
    }
    ENDCG
)
Fallback "Diffuse"

)

This poor little shader, there’s an error on almost every line. () and {} Scopes are all broken. The’s also alot of typos. #Pragma needs to be #pragma, lambert to Lambert, etc. You can avoid these by creating a new shader in Unity. Assets->Create->Shader. All that gets generated for you.

After that, all that was needed was to create a _Color property and multiply it with MainTex.

Shader "CTD/SimpleDiffuse" {
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
		_Color("Color Tint", Color) = (1,1,1,1) 
	}
	SubShader {
		Tags { "RenderType"="Opaque" }
		LOD 200
		
		CGPROGRAM
		#pragma surface surf Lambert

		sampler2D _MainTex;
		fixed4 _Color;
		
		struct Input {
			float2 uv_MainTex;
		};

		void surf (Input IN, inout SurfaceOutput o) {
			half4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
			o.Albedo = c.rgb;
			o.Alpha = c.a;
		}
		ENDCG
	} 
	FallBack "Diffuse"
}