try,
Code:
Public Class Form1
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
ColorWord(RichTextBox1, "Blue", Color.Blue)
ColorWord(RichTextBox1, "Red", Color.Red)
End Sub
Public Sub ColorWord(rtb As RichTextBox, word As String, color As Color)
Dim start, found As Integer
With rtb
found = .Find(word, start, RichTextBoxFinds.WholeWord Or RichTextBoxFinds.NoHighlight)
Do While found > -1
.SelectionStart = found
.SelectionLength = word.Length
.SelectionColor = color
start = found + word.Length
If start >= .TextLength Then Exit Do
found = .Find(word, start, RichTextBoxFinds.WholeWord Or RichTextBoxFinds.NoHighlight)
Loop
End With
End Sub
End Class