Yellowing top of plant

new growth is usually a bit lighter when it first comes out.. however especially when she's growing a lot, don't forget to ensure to provide the nitrogen and other nutrient demands during that time.. also it seems you have just shifted from grow nutrients to bloom... this should normally be done after the initial stretching phase at the beginning of the blooming phase. bloom nutrients are low in nitrogen, while the plant still needs it for growth. the shift over to bloom-nutrients should be done, when the plant stops growing in length and starts focusing on building the buds, which is when she needs more P and K and usually around the end of the 2nd week of bloom (depending on the strain).. while i don't think you have an actual nitrogen deficiency, i think the lower levels just make her brighter.. Nitrogen plays a big part in the "green-ness" of the leaves (heavy doses/too much would make them dark green)