I think he meant RichString library. Here is an example that will work for you:
B4X:
Dim rs As RichString
Dim txtTest as Edittext
rs.Initialize("{Blue}ks{Blue}{Red}droid{Red}")
rs.Color2(Colors.Blue,"{Blue}")
rs.Color2(Colors.Red, "{Red}")
rs.BackColor(Colors.Yellow,2,7)
txtTest.Text = rs 'will highlight droid yellow