Import to excel using Excel buffer with different font color

[a bit offtopic]
I believe it's export to excel you mean.
Usually the functions in NAV that communicate with external programs are from NAV's point of view. Export to <program> from NAV, or import from <program> to NAV.
[/a bit offtopic]

The excel buffer does not support different fonts/colors/backcolors out of the box. But the excel automation does support these. Since the excel buffer uses the Excel automation, it shouldn't be a too hard of a challenge to modify the excel buffer with support for these. Ofcourse you can also just use the excel automation directly in your report. However I'd suggest modifying the exel buffer, so that when the customer is satisfied with the export and requests other reports to have the same functionality, you don't have to copy paste your code.

However, since you're posting in Three Tier forum, the excel buffer performs worse on RTC than on the classic client.
You'll find topics adressing this issue, feel free to consult these.