Very simply lit shader for particle system that uses vertex/particle system colour

NormalDotLight.shader

Shader "NewChromantics/NormalDotLight"
{
	Properties
	{
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100
		Cull Off
		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag

			#include "UnityCG.cginc"
			#include "UnityLightingCommon.cginc" // for _LightColor0

			struct v2f
			{
				float4 vertex : SV_POSITION;
				float3 Colour : COLOR;
				float Light : TEXCOORD0;
			};


			v2f vert (appdata_full v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				float3 worldNormal = UnityObjectToWorldNormal(v.normal);
				o.Light = dot(worldNormal, _WorldSpaceLightPos0.xyz);
				o.Colour = v.color;
				return o;
			}

			fixed4 frag (v2f i) : SV_Target
			{
				float3 Rgb;
				if ( i.Light < 0 )
				{
					float Shadow = -i.Light;
					Rgb = lerp( i.Colour, float3(0,0,0), Shadow);
				}
				else
				{
					float Light = i.Light * i.Light* i.Light;
					Rgb = lerp( i.Colour, float3(1,1,1), Light);
				}
				return float4(Rgb,1);
			}
			ENDCG
		}
	}
}