I spent AGES working thru this one and couldn't find it anywhere!
The basic problem is that you have to update the richtextbox.rtf, not .text.
And it is very fussy about goes in there!!
A quick and dirty method is to set the richtextbox.text to a value such as "WHATEVER" and then replace that in the richtextbox.rtf with your rtf enabled code. As for what .rtf recognises in formatting, I resorted to copying and pasting rtf into the richtextbox and then looking at the .rtf value.
I only wanted a bit of bold!! By the time I had sorted it out I had decided on a different display method anyway so I hope someone uses this so I haven't wasted my time!!
The working code from my project, before I dump it:
richtextbox.Text =
"REPLACETHIS"
Do While Not EOF(1)
Input(1, aLine)
info = Split(Replace(aLine, "\", "\\"), ",")
TempInfo = TempInfo & "\b Result Displayed: \b0" & info(1) & " \par " & "\b URL: \b0 " & info(0) & " \par " & "\b Interval: \b0 " & info(2) & " \par " & "\b Log Path: \b0 " & info(3) & " \par " & " \par "
Loop
richtextbox.Rtf = Replace(richtextbox.Rtf, "REPLACETHIS", TempInfo)
I've just done bolds and replaced the slashes as I was showing URLs and file paths.