ちょこっといじったらトゥーンの影色変えるシェーダーできるな。
Toon-Lightedのシェーダー開いて名前変えて保存。

Shader "Toon/LightedShadows" {←書き換え
Properties {
_Color ("Main Color", Color) = (0.5,0.5,0.5,1)
_ShadowColor("Shadow Color",Color)=(0.5,0.5,0.5,1)←書き足し
_MainTex ("Base (RGB)", 2D) = "white" {}
_Ramp ("Toon Ramp (RGB)", 2D) = "gray" {}
}
SubShader {
Tags { "RenderType"="Opaque" }
LOD 200
CGPROGRAM
#pragma surface surf ToonRampShadow←書き変え
sampler2D _Ramp;
// custom lighting function that uses a texture ramp based
// on angle between light direction and normal
#pragma lighting ToonRampShadow exclude_path:prepass←書き換え
float4 _ShadowColor;←書き足し
inline half4 LightingToonRampShadow (SurfaceOutput s, half3 lightDir, half atten)
{
#ifndef USING_DIRECTIONAL_LIGHT
lightDir = normalize(lightDir);
#endif
half d = dot (s.Normal, lightDir)*0.5 + 0.5;
half3 ramp = tex2D (_Ramp, float2(d,d)).rgb;
half4 c;
c.rgb = s.Albedo * _LightColor0.rgb * ramp ;←書き換え
c.rgb*= d * min((atten + _ShadowColor.rgb), 1); ←書き足し
後略