colors - How to colorize specific strings in powershell textbox

How to colorize specific strings in text box in powershell forms. I don't use any "studio" applications.

Output for example:

Searching...
a - found
b - Not found
c - found

Expected result:

Searching...
a - found
b - \red\Not found\red\
c - found

I heard about RichTextBox, but when using the code bellow it doesn't print anything, just an empty string(no errors appeared from code)

$StatisticsBox = New-Object System.Windows.Forms.RichTextBox 
    $StatisticsBox.Location = New-Object System.Drawing.Size(170,30) 
    $StatisticsBox.Size = New-Object System.Drawing.Size(150,320) 
    $StatisticsBox.MultiLine = $True 
    $StatisticsBox.ScrollBars = "Vertical" 
    $StatisticsBox.ReadOnly=$True
    $Form.Controls.Add($StatisticsBox) 

$StatisticsBox.SelectionColor = 'red' <---- also tried "color.red"
$StatisticsBox.text = "`r`nNot Found:`r`n" + $StatisticsBox.AppendText("colored stirng") + "`r`n" +$StatisticsBox.text