Screw head "weeps"

I sanded my deck to remove a peeling deck "paint". I rinsed the deck well and now have to go back and sand the low spots and around some screw heads to get the rest of it off. My issue is the deck is already graying before I can finish the hand sanding. Can I stain or does the deck need to look like new the way it did after sanding? How consistent does the surface "color" need to be in order for me to get a good finish? Is there an easy way of getting rid of this new gray?