Could painting my room a brighter color help with my sad?

Don't think so. Need the right light and use it to extend daylight am & pm.
Yes, try lite yellow. Yes, it's possible. What is most helpful for SAD (Seasonal Affective Disorder) is additional light. There are many alternatives for therapeutic light source. Getting more time outside in the sun is very helpful. This disorder is most prevalent in the winter, when days are short and often grey and cloudy. You should also consider CBT psychotherapy from an experienced psychologist. Good luck!
Worth a try! Brightness and color are important for typical sad. Most sad is prominent in winter months when sun shines for fewer hours and is less bright on the lower horizon. Keeping brighter lights on during normal waking hours is helpful. Get out in the sun whenever possible. There is some evidence that vit d can help. Perhaps losses that have occured in winter are partly to blame. Check it out.I.