也容易，如果是黑白三个颜色加上相同的渐变量，彩色的是起始颜色的三个分量与终止颜色的对应三个分量的差值，再除于相同的份数，就得出三原色各自的步进量。
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窗体上放个图片框试试下面代码：
Private Sub PictureBox1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint
Dim startColor As Color = Color.Red
Dim endColor As Color = Color.Green
Dim s As String = "vb.net 如何使文字能渐变颜色，就是颜色慢慢变淡然后在慢慢恢复？"
Dim Steps As Integer = s.Length \ 2
Dim StepR As Integer = (CInt(endColor.R) - startColor.R) \ Steps
Dim StepG As Integer = (CInt(endColor.G) - startColor.G) \ Steps
Dim StepB As Integer = (CInt(endColor.B) - startColor.B) \ Steps
Dim R As Integer = startColor.R
Dim G As Integer = startColor.G
Dim B As Integer = startColor.B
Dim drawFont As New System.Drawing.Font("Arial", 16)
Dim X As Integer = 50
For i As Integer = 1 To Steps
Dim drawBrush As New SolidBrush(Color.FromArgb(R, G, B))
e.Graphics.DrawString(s.Substring(i - 1, 1), drawFont, drawBrush, X, 50.0)
X += 18
R += StepR
G += StepG
B += StepB
Next
For i As Integer = 1 To Steps
Dim drawBrush As New SolidBrush(Color.FromArgb(R, G, B))
e.Graphics.DrawString(s.Substring(i + Steps - 1, 1), drawFont, drawBrush, X, 50.0)
X += 18
R -= StepR
G -= StepG
B -= StepB
Next
End Sub
VB可使用Point方法来获取图片指定点的颜色。
Point 方法
按照长整数，返回在 Form 或 PictureBox 上所指定磅的红-绿-蓝 (RGB) 颜色。
语法
object.Point(x, y)
'窗体判色代码:
Private Sub Form1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
Text1 = X
Text2 = Y
Text3 = Point(X, Y)
Text4 = (Val(Text3) Mod 65536) Mod 256 'Red
Text5 = (Val(Text3) Mod 65536) \ 256 'Green
Text6 = Val(Text3) \ 65536 'Blue
Shape1.FillColor = RGB(Val(Text4), Val(Text5), Val(Text6))
End Sub
'PictureBox判色代码:
Private Sub Picture1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
Text1 = X
Text2 = Y
Text3 = Picture1.Point(X, Y)
Text4 = (Val(Text3) Mod 65536) Mod 256 'Red
Text5 = (Val(Text3) Mod 65536) \ 256 'Green
Text6 = Val(Text3) \ 65536 'Blue
Shape1.FillColor = RGB(Val(Text4), Val(Text5), Val(Text6))
End Sub
Label控件是没有办法实现多种颜色的文字的，只能用RichTextBox来实现，而且你的自定义格式字符串也没有结尾的，这样很不好，至少也要red红色字/redyellow黄色字/yellow，而且实现也很麻烦的，下面的代码我没有检测正确性，有错误的自己改一改吧
Dim colortag() as string
dim colors() as color
const txt as string="red红色字/redyellow黄色字/yellow"
private sub Form_Load(object sender,eventargs e)handles mybase.load
colortag(0)="red":Colortag(1)="yellow"
colors(0)=color.red:colors(1)=color.yellow
richtextbox1.text=txt
for i as integer=0 to colortag.lenght-1
dim tag as string="" colortag(i) ""
dim endtag as string="/" colortag(i) ""
dim find as integer=1
do
find=instr(find,txt,tag)+tag.lenght
if(find0)then
dim find1 as integer=instr(find,txt,endtag)
richtextbox1.SelectionStart=find
richtextbox1.selectionlenght=find1-find
richtextbox1.selectioncolor=colors(i)
find=find1
else
exit do
end if
loop
next
end sub
绘制线条采用Draw开头的方法，颜色参数用Pen类；
绘制有填充色的封闭图形采用Fill开头的方法，颜色参数用Brush类；
例如：
'绘制一个实心圆，该圆在：直线x=200，y=200，x=200+100，y=200+100所划矩形区域内
Me.CreateGraphics.FillEllipse(New SolidBrush(Color.Orange), 200, 200, 100, 100)
'绘制一个空心圆，该圆在：直线x=200，y=200，x=200+100，y=200+100所划矩形区域内
Me.CreateGraphics.DrawEllipse(New Pen(Color.Black), 200, 200, 100, 100)