You want to include color information in an OutputStream, but OutputStreams don't naturally contain color information. You need to depend upon wherever your stream is going to make the color happen. Some places that read the content of an OutputStream may be able to recognize certain codes and display colors based on those codes, but there is nothing universal.
bguild has already answered your question.
Your writer just writes characters to the output stream. Characters do not have fonts, colors, or anything else, they are just characters.
Depending on where your file is displayed, characters in the file may be interpreted as formatting information according to some standard, eg RTF or HTML. That depends on on how and where the file is being displayed. There is no problem writing RTF or HTML codes to your file, if that's appropriate