Where are you executing the code? This worked:
protected void TreeView1_Load(object sender, EventArgs e)
{
TreeView1.Nodes[0].Text = "<font color='Red'>Red</font>";
TreeView1.Nodes[1].Text = "<font color='Blue'>Blue</font>";
TreeView1.Nodes[2].Text = "<font color='Green'>Green</font>";
}
Steve Wellens