The problem about Color In C#!

Questions & Answers
1

I got a script with C#.For example:
This is one function in the script.

 void OnShow(){
   Color C1=new Color(0.5,0.5,0.5,0.5);
   Color C2=new Color(0.75,0.75,0.75,0.75);

   LineRenderer LineRender=(LineRenderer)GetComponent(LineRenderer);
   LineRender.material=new Material("Particle/Additive");

`` LineRender.SetColors(C1,C2);
}

It Shows errors:
err1502:The best OverLoadedmethod match for "UnityEngine.Color.Color(float,float,float,float)" has some invalid arguments;
err1503:Argument "#1" cannot convert "double" expression type "float".

why do those errors happen?
"0.5" should be "float"! Is it "Double"?
I can not get it?
Please help me....
I am very tangle....
2

float = 1.0