Colors - soothing (earth tones)
Lighting - soft
Overall, you want to create a warm, cozy, inviting space so they won't say "office" right away. You should also stage it as a bedroom so they can see that it fits the furniture and can be practical despite being a little quirky. You might also consider playing up the funkiness, by decorating to stay with a funky feel - they might just love it!
If you are currenlty using this room as an office, and have a need to continue in it's current use, what modificaitons might you make that could soften the room? i.e. put away stacks of books, office supplies, or office tools that aren't needed daily. Use accent soft lighting, add throw pillows on chairs/sofas.
Depending upon your current use of the room, you might be able to completely change the furnishings. Arrange the furniture to soften the presentation and add items that promote comfort/relaxation.
Ask your Realtor about calling in a stager.
Is your home listed with a Realtor?
Remember that homes listed with a Realtor sell for an average of 16% more than homes that are sold directly by the owner without professional representation.
My concern is that if this basic issue was overlooked, you may have other issues that could affect how buyers perceive the value of your property. In some markets home staging is almost critical!
Good luck, and Merry Christmas!