Purple'ish hues on leaves

The autumn colors are from cooler temperatures at night and/or genetics. Looks liek thy are also paling from tip-in .. if this is also progressing up the plant, it's needing more nitrogen. unlike what often gets repeated ad nauseum, a flowering plant most definitely needs nitrogen at nearly the same levels as in vege phase. if you want your plant to turn yellow, stick to teh culturally-constructed nonsense that's never once been supported with evidence :P