Yellow is a cheerful balance to purple which has a tendency to be oppressive. Purple is very deep and rich and can sometimes be overwhelming. Yellow lifts the mood and is a perfect counterbalance.
Yellow is the symbol of warmth, energy. Yellow encourages happy feelings and actually helps depressive moods.
Purple is associated with spirituality. It is the symbol of royalty. Purple can encourage creativity and imagination. Lighter purples are more romantic and delicate.