Next, grab your brown paint and paint the entire fence. It's easiest to lay the sections on a couple drop cloths and use a sprayer. If you have many hands to make light work, consider yourself lucky and grab the old paint brushes.
When your newly assembled fence sections are dry, dry brush (remove most of the paint before brushing) various areas of the fence with the gray paint. Experiment and see what you like.
Another possibility: It's hard to see in the second pic, but the cross tombstone was painted different shades of gray and then painted white. When the white paint was getting close to being dry, I sprayed and misted it with water. This washed away and thinned the white paint which reveals some of the grays. I think you could have a nasty white picket fence if you paint the fence brown first, then applied the white paint technique. Might be worth a try.