Colored pistils are usually genetics, and not indicative of any problem. Unless of course they just burned from the light being too close, but probably wouldn't turn an exotic color like pink or purple. Consider yourself lucky. One of my first grows had pink pistils and many experienced growers said they had never seen anything like it. When you say red at the center of the leaves, do you mean the veins or the actual leaves themselves? Either way that too can be genetic, or an indicator of a magnesium deficiency. Probably the former, mag defs aren't too common, it's added to most nutes and soils on some scale. Don't worry man, if something is wrong you will get burnt looking leaves, or drooping, or stunted growth. Just enjoy the little nuances of personality your girl is showing you, most cannabis plants won't stay just green.