setting color on a part of a line in word using c#

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C#5.0

MS-Word

I can't find a solution on how change the color of a part of a line.
It should have to do with a selection of a rang.text.
Like para.Range.Text = "Chrysanthemum Curve";
And making the part 'Curve' blue.

// Modify to suit your machine:
// Get the Word application object.
Word._Application word_app = new Word.Application();

// Make Word visible (optional).
word_app.Visible = true;
object oEndOfDoc = "\\endofdoc";
// Create the Word document.
object missing = Type.Missing;
Word._Document word_doc = word_app.Documents.Add(
    ref missing, ref missing, ref missing, ref missing);

// Create a header paragraph.
Word.Paragraph para = word_doc.Paragraphs.Add(ref missing);
para.Range.Text = "Chrysanthemum Curve";
//para.Range.Text = "Curve";
object style_name = "Heading 1";
para.Range.set_Style(ref style_name);
para.Range.InsertParagraphAfter();

// Add more text. Curve"
para.Range.Text = "To make a chrysanthemum curve, " +
    "use the following parametric equations as t goes " +
    "from 0 to 21 * ? to generate " +
    "points and then connect them.";
para.Range.InsertParagraphAfter();
string qa = "";
qa = para.Range.Text.Substring(1, 2);
// Save the current font and start using Courier New.
string old_font = para.Range.Font.Name;
para.Range.Font.Name = "Courier New";
para.Range.Font.ColorIndex = Microsoft.Office.Interop.Word.WdColorIndex.wdByAuthor;

// Add the equations.
para.Range.Text =
    "  r = 5 * (1 + Sin(11 * t / 5)) -\n" +
    "      4 * Sin(17 * t / 3) ^ 4 *\n" +
    "      Sin(2 * Cos(3 * t) - 28 * t) ^ 8\n" +
    "  x = r * Cos(t)\n" +
    "  y = r * Sin(t)";

// Start a new paragraph and then
// switch back to the original font.
para.Range.InsertParagraphAfter();
para.Range.Font.Name = old_font;