Selectable.transition

Description

The type of transition that will be applied to the targetGraphic when the state changes.

using UnityEngine;
using System.Collections;
using UnityEngine.UI; // Required when Using UI elements.

public class ExampleClass : MonoBehaviour
{
    public Button btnMain;

    void SomeFunction()
    {
        //Sets the main button's transition setting to "Color Tint".
        btnMain.transition = Selectable.Transition.ColorTint;
    }
}