使用方法：Color.FromArgb(Int32，Color)
 第一个参数代表透明度，数值在0-255之间
 
 选中button将属性“FlatStyle”设置为：“Flat”
 
在***.Designer.cs中加入以下代码
 
this.OpenFileButton.BackColor = System.Drawing.Color.FromArgb(255, Color.Crimson);
this.NextButton.BackColor = System.Drawing.Color.FromArgb(100, Color.Crimson);  
 

 
 效果图：
 

 
1.backcolor属性为color.FromArgb(100, 220, 220, 220);
 
 
2.全透明设置为transparent方法。
 
转载于:https://www.cnblogs.com/gaara-zhang/p/9133335.html

前言
 
由于项目需求需要用到透明控件。但是，winform项目的控件透明都是将父控件的图像绘制成子控件的背景来实现的，这种透明存在很大的问题，不合格。
 然后，我想到wpf在透明这块做的比较好，想是不是可以在winform中使用wpf控件来实现，结果发现还是走不通，由于elementhost控件是winform中的控件，而wpf控件必须要用它来承载才能在winform中实现，不合格。
 最后，百度发现了使用Region实现透明控件，Region透明控件主要是设置控件的绘制区域来实现的透明控件，所以也不能说是透明控件，只能说是只绘制控件的非透明部分来达到透明的效果，不过基本能够满足我的需求。效果图如下：
 
 
最后
 
这个存在的问题是未绘制区域，就无法触发控件的点击事件，点击的时候会直接点击到后面的控件上。目前没有找到更好的实现方法，之前百度的时候看到有说最好的办法是使用directx重写控件，不过这个方法对本人来说有点复杂了。如果大家有更好的实现方法，欢迎交流。

使用BackColor=Color.Translate这种方法只能实现和背景色一样但是不是真的透明，控件后面的控件还是看不到
 
1.首先写一个基类
 
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
using System.ComponentModel;
 
namespace CYControls
{
    /// <summary>
    /// 提供透明和旋转功能的基础控件
    /// </summary>
    public class CYBaseControl : Control
    {
        private float _iBorderThickness = 1f;
        private float _iOpacity = 1f;
        private Brush _brushBg = null;
        private Pen _penFg = null;
 
        public CYBaseControl()
        {
            this.SetStyle(ControlStyles.SupportsTransparentBackColor |
                ControlStyles.Opaque, true);
            this.BackColor = Color.Transparent;
            BackgroundBrush = Brushes.Transparent;
            ForegroundPen = Pens.Black;
        }
 
        #region Propertys
        #region HideParent
        [Browsable(false)]
        [EditorBrowsable(EditorBrowsableState.Never)]
        public override string Text
        {
            get { return base.Text; }
            set { base.Text = value; }
        }
 
        [Browsable(false)]
        [EditorBrowsable(EditorBrowsableState.Never)]
        public override Image BackgroundImage
        {
            get { return base.BackgroundImage; }
            set { base.BackgroundImage = value; }
        }
 
        [Browsable(false)]
        [EditorBrowsable(EditorBrowsableState.Never)]
        public override ImageLayout BackgroundImageLayout
        {
            get
            {
                return base.BackgroundImageLayout;
            }
            set
            {
                base.BackgroundImageLayout = value;
            }
        }
        #endregion
 
        public override Color BackColor
        {
            get
            {
                return base.BackColor;
            }
            set
            {
                base.BackColor = value;
                ResetBgBrush();
            }
        }
 
        //[EditorAttribute(typeof(BrushTypeEditor), typeof(System.Drawing.Design.UITypeEditor))]  
        //public double Background
        //{
        //    get;
        //    set;
        //}
 
        public override Color ForeColor
        {
            get
            {
                return base.ForeColor;
            }
            set
            {
                base.ForeColor = value;
                ResetFgPen();
            }
        }
 
        public float BorderThickness
        {
            get { return _iBorderThickness; }
            set
            {
                if (value < 0)
                {
                    throw new Exception("Out off range");
                }
                _iBorderThickness = value;
                ResetFgPen();
                ResetDrawRect();
            }
        }
 
        public virtual float RotateAngle
        {
            get;
            set;
        }
 
 
        public float Opacity
        {
            get { return _iOpacity; }
            set
            {
                if (value > 1 || value < 0)
                {
                    throw new Exception("Out of range,the Value be in [0,1]");
                }
                else
                {
                    _iOpacity = value;
                    ResetBrushes();
                }
            }
        }
 
        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle = 0x20;
                return cp;
            }
        }
 
        protected virtual Brush BackgroundBrush
        {
            get { return _brushBg; }
            set { _brushBg = value; }
        }
 
        protected virtual Pen ForegroundPen
        {
            get { return _penFg; }
            set { _penFg = value; }
        }
 
        protected virtual RectangleF DrawRect
        {
            get;
            set;
        }
        #endregion
 
        #region Methods
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
        }
 
        protected override void OnSizeChanged(EventArgs e)
        {
            base.OnSizeChanged(e);
            ResetDrawRect();
        }
        protected override void OnPaddingChanged(EventArgs e)
        {
            base.OnPaddingChanged(e);
            ResetDrawRect();
        }
 
        protected void ResetBrushes()
        {
            ResetBgBrush();
            ResetFgPen();
        }
 
        protected void ResetBgBrush()
        {
            BackgroundBrush = new SolidBrush(GetOpacityColor(BackColor, Opacity));
        }
 
        protected void ResetFgPen()
        {
            ForegroundPen = new Pen(GetOpacityColor(ForeColor, Opacity), BorderThickness);
        }
 
        protected Color GetOpacityColor(Color baseColor, float op)
        {
            return Color.FromArgb(Convert.ToInt32(op * baseColor.A), baseColor);
        }
 
        private void ResetDrawRect()
        {
            float dbwidth = 2 * BorderThickness;
            float halfwidth = BorderThickness / 2;
            int paddingWhith = Padding.Left   Padding.Right;
            int paddingHeight = Padding.Top   Padding.Bottom;
            if (dbwidth > Width - paddingWhith || dbwidth > Height - paddingHeight)
            {
                DrawRect = this.Bounds;
            }
            else
            {
                DrawRect = new RectangleF(Padding.Left   halfwidth,
                    Padding.Top   halfwidth,
                    Width - BorderThickness - paddingWhith,
                    Height - BorderThickness - paddingHeight);
            }
        }
        #endregion
    }
}
 
2.创建RectangleShape
 
public class RectangleShape:CYBaseControl
{
    protected override void OnPaint(System.Windows.Forms.PaintEventArgs e)
    {
        base.OnPaint(e);
        e.Graphics.FillRectangle(BackgroundBrush,this.ClientRectangle);
        e.Graphics.DrawRectangle(ForegroundPen,Rectangle.Round(this.DrawRect));
    }
}
 
3.应用实例
 
RectangleShape recS=new RectangleShape ();
recS.Name="TestShape";
recS.Height=100;
recS.Width=100;
recS.BackColor=Color.Transparent;
recS.Location=new Point(0,0);
//设置透明度
recS.Opacity=0.5F;
//把自定义的这个控件添加到需要的容器中
**.Controls.Add(recS);