本文实现了三种颜色匹配的方法，
一，先将Color结构的颜色转换为HSB颜色，然后再对其进行匹配比较，这是目前为止比较准确的一种方法，得到的颜色近似度很高
二，比较两个Color结构颜色的RGB分量的差的绝对大小，设定一个阈值，选出最为接近的一个，这种方法精度不高，有些颜色会有很明显的失真，但速度较快
三，比较两个Color结构颜色的RGB分量的差的平方和的大小，得到容差，最好选出容差最小的一个，这种方法精度比（二）高，速度比（一）快
笔者用的第一种方法，对256颜色匹配的非常好，其中三种方法的代码(VB.Net)如下，大家一看便知如何应用

#Region "先转换成hsb颜色，再进行匹配，最为准确的颜色匹配方法"  
  ''' <summary>
  ''' hsb颜色类，相当于一个结构
  ''' </summary>
  ''' <remarks></remarks>
  Class HSB
    Public Hue As Double
    Public Saturation As Double
    Public Brightness As Double
    Sub New(ByVal h As Double, ByVal s As Double, ByVal b As Double)
      Hue = h
      Saturation = s
      Brightness = b
    End Sub
  End Class
''' <summary>
  ''' rgb转换为hsb
  ''' </summary>
  ''' <param name="red"></param>
  ''' <param name="green"></param>
  ''' <param name="blue"></param>
  ''' <returns></returns>
  ''' <remarks></remarks>
  Private Function RGBtoHSB(ByVal red As Integer, ByVal green As Integer, ByVal blue As Integer) As HSB
    Dim r As Double = red / 255.0
    Dim g As Double = green / 255.0
    Dim b As Double = blue / 255.0
    Dim max As Double = Math.Max(r, Math.Max(g, b))
    Dim min As Double = Math.Min(r, Math.Min(g, b))
    Dim h As Double = 0.0
    If (max = r And g >= b) Then
      h = 60 * (g - b) / (max - min)
    ElseIf (max = r And g < b) Then
      h = 60 * (g - b) / (max - min) + 360
    ElseIf (max = g) Then
      h = 60 * (b - r) / (max - min) + 120
    ElseIf (max = b) Then
      h = 60 * (r - g) / (max - min) + 240
    End If
    Dim s As Double
    If max = 0 Then
      s = 0.0
    Else
      s = 1.0 - (min / max)
    End If
    Return New HSB(h, s, max)
 End Function
 
''' <summary>
  ''' 获得最为接近的索引颜色
  ''' </summary>
  ''' <param name="color">所比较的颜色</param>
  ''' <param name="LabelColorsHSB">颜色列表</param>
  ''' <returns>返回与所比较的颜色最为接近的颜色在颜色列表中的索引值</returns>
  ''' <remarks></remarks>
  Private Function GetNearestColorLabelIndex(ByVal color As Color, ByVal LabelColorsHSB As List(Of HSB)) As Integer
    Const weightHue As Double = 0.8
    Const weightSaturation As Double = 0.1
    Const weightValue As Double = 0.1
    Dim minDistance As Double = Double.MaxValue
    Dim minIndex As Integer = 255
    Dim targetHSB As HSB = RGBtoHSB(color.R, color.G, color.B)
    For i As Integer = 0 To LabelColorsHSB.Count - 1
      Dim dH As Double = LabelColorsHSB(i).Hue - targetHSB.Hue
      Dim dS As Double = LabelColorsHSB(i).Saturation - targetHSB.Saturation
      Dim dV As Double = LabelColorsHSB(i).Brightness - targetHSB.Brightness
      Dim curDistance As Double = Math.Sqrt(weightHue * Math.Pow(dH, 2) + weightSaturation * Math.Pow(dS, 2) + weightValue * Math.Pow(dV, 2))
      If (curDistance < minDistance) Then
        minDistance = curDistance
        minIndex = i + 1
      End If
    Next
    Return minIndex
  End Function

#End Region

#Region "绝对值容差，设置阈值得到匹配颜色"
  ''' <summary>
  ''' 得到相近的color
  ''' </summary>
  ''' <param name="pColor">所匹配颜色</param>
  ''' <returns></returns>
  ''' <remarks></remarks>
  Public Function GetCloseColor(ByVal pColor As Color,Byavl ColorList As List(of Color)) As Integer
    Dim pColorDis As Integer = Const_ColorDistance
    Dim Dif As Integer
    Dim pACIcolor As Integer = Const_DefaultColorIndex
    For i As Integer = 0 To ColorList.Count - 1
      ''绝对值容差法
      Dif = Math.Abs(ColorList(i).R - pColor.R) + Math.Abs(ColorList(i).G - pColor.G) + Math.Abs(ColorList(i).B - pColor.B)
      If Dif < pColorDis Then
        pColorDis = Dif
        pACIcolor = i + 1
      End If
    Next
    Return pACIcolor
  End Function
#End Region

#Region "平方容差选择最小值得到匹配颜色"

  ''' <summary>
  ''' 平方容差选择最小值得到匹配颜色
  ''' </summary>
  ''' <param name="pColor">所匹配颜色</param>
  ''' <returns></returns>
  ''' <remarks></remarks>
  Private Function GetCloseColor(ByVal pDC As Color,Byavl ColorList As List(of Color)) As Integer
    Dim pACIcolor As Integer = Const_DefaultColorIndex
    Dim pDifs As New List(Of Long)
    Dim pHash As New Hashtable
     For i As Integer = 0 To ColorList.Count - 1
      Dim tCompValue As Long
      tCompValue = ColorValueComp(RGB(pDC.R, pDC.G, pDC.B), RGB(ColorList(i).R, ColorList(i).G, ColorList(i).B))
      pDifs.Add(tCompValue)
      If Not pHash.Contains(tCompValue) Then pHash.Add(tCompValue, i + 1)
    Next
    pDifs.Sort()
    pACIcolor = pHash(pDifs(0))
    Return pACIcolor
  End Function

    ''' <summary>
    ''' 判断两个color在容差范围内是否相似
    ''' </summary>
    ''' <param name="pColorA">颜色A</param>
    ''' <param name="pColorB">颜色B</param>
    ''' <param name="pValve">容差</param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Private Function ColorValueIsBorder(ByVal pColorA As Long, ByVal pColorB As Long, ByVal pValve As Long) As Boolean
      '在容差pValve的范围内，比较两个颜色是否近似。
      Dim tOutValue As Boolean
      Dim tCompValue As Long
      tCompValue = ColorValueComp(pColorA, pColorB)
      If tCompValue <= pValve Then
        tOutValue = True
      Else
        tOutValue = False
      End If
      Return tOutValue
    End Function
    ''' <summary>
    ''' 通过Value值获得color
    ''' </summary>
    ''' <param name="pColorValue">Value值</param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Private Function ColorGetByValue(ByVal pColorValue As Long) As Color
      '从一个Long类型的颜色数据获得一个ColorRGB类型。
      Dim tOutColor As Color = Color.FromArgb(255, pColorValue Mod 2 ^ 8, (pColorValue \ 2 ^ 8) Mod 2 ^ 8, (pColorValue \ 2 ^ 16) Mod 2 ^ 8)
      Return tOutColor
    End Function
    ''' <summary>
    ''' 获得两种long类型颜色的容差
    ''' </summary>
    ''' <param name="pColorA">颜色A</param>
    ''' <param name="pColorB">颜色B</param>
    ''' <returns></returns>
    ''' <remarks></remarks>
    Public Function ColorValueComp(ByVal pColorA As Long, ByVal pColorB As Long) As Long
      '获得两个Long类型颜色的色差。
      Dim tOutValue As Long
      Dim tColorA As Color
      Dim tColorB As Color
      tColorA = ColorGetByValue(pColorA)
      tColorB = ColorGetByValue(pColorB)
      tOutValue = ColorRGBComp(tColorA, tColorB)
      Return tOutValue
    End Function
    ''' <summary>
    ''' 获得两种颜色之间的容差
    ''' </summary>
    ''' <param name="pColorA">颜色A</param>
    ''' <param name="pColorB">颜色B</param>
    ''' <returns></returns>
    ''' <remarks>平方容差法</remarks>
    Public Function ColorRGBComp(ByRef pColorA As Color, ByRef pColorB As Color) As Long
      '获得两个ColorRGB的色差。
      Dim tOutValue As Long
      Dim tAbsR As Long
      Dim tAbsG As Long
      Dim tAbsB As Long
      tAbsR = Math.Abs(CLng(pColorA.R) - CLng(pColorB.R))
      tAbsG = Math.Abs(CLng(pColorA.G) - CLng(pColorB.G))
      tAbsB = Math.Abs(CLng(pColorA.B) - CLng(pColorB.B))
      tOutValue = Math.Sqrt(tAbsR ^ 2 + tAbsG ^ 2 + tAbsB ^ 2)
      Return tOutValue
    End Function
 #End Region