若要同时保留上一个脱字符号位置和选取范围：

... Call to suspend drawing here 

var start = richTextBox1.SelectionStart;
var len = richTextBox1.SelectionLength;

richTextBox1.Select(10, 3); 
richTextBox1.SelectionBackColor = Color.White;

richTextBox1.SelectionStart = start;
richTextBox1.SelectionLength = len;

... Call to resume drawing here

要防止闪烁，请检查此帖子中提供的解决方案：https://stackoverflow.com/a/487757/6630084
TextBoxBase.SelectionStart Property
TextBoxBase.SelectionLength Property

您可以在设置颜色之前存储光标位置，然后按如下方式恢复位置：

Public Sub New()
    InitializeComponent()
    richTextBox1.Text += "RichTextBox text line 1" & Environment.NewLine
    richTextBox1.Text += "RichTextBox text line 2" & Environment.NewLine
    richTextBox1.Text += "RichTextBox text line 3" & Environment.NewLine

    Dim i As Integer = richTextBox1.SelectionStart
    Dim j As Integer = richTextBox1.SelectionLength

    richTextBox1.Select(10, 3)
    richTextBox1.SelectionBackColor = Color.White

    richTextBox1.SelectionStart = i
    richTextBox1.SelectionLength = j 'use this to preserve selection length, or
    richTextBox1.SelectionLength = 0 'use this to clear the selection
End Sub