Keyword Text Color Change

You'll have to use a RichTextBox for this as I think I'm right in saying that the ordinary TextBox can only support one color at a time but, subject to that, this code should get you on the right track:

richTextBox1.Text = "The quick brown fox jumped over the lazy dog";

string keyword = "brown";

int index = richTextBox1.Find(keyword);

richTextBox1.SelectionStart = index;

richTextBox1.SelectionLength = keyword.Length;

richTextBox1.SelectionColor = Color.Brown;

richTextBox1.SelectionLength = 0;

richTextBox1.SelectionStart = richTextBox1.Text.Length;