Yellow is complementary colour to purple. This means they are opposite on the colour wheel. They contrast and usually go very well together. Green is neither supplementary, complementary or analogous meaning it very rarely goes well with purple unless blue is the primary colour. Colours that can easily go well with purple are blue, red, and or yellow. I don't recommend using all 4 colours but having 2 supplementary colours such as purple and blue with either yellow or orange. This colour scheme is known as a split complementary and in my opinion split complementary colour schemes are far more pleasing to the eye than normal complementary schemes. I recommend orange because it is complementary to blue. Anyways, that is your art theory lesson on the colour wheel.