It has too low contrast and is quite hard to read because of all the details..
There's not much depth in there, except for the edges, but the effect is very subtle, which also makes it hard to tell what it actually is.
Are each tile going to have a gameplay purpose or is it just for variation? Is it important for the gameplay that you can see the tile grid?
It still looks rather abstract. I mean, I can tell that it's bricks and glass, but is it a rooftop or?
Also, why not give a perspective to the gems by making them taller and floating with a shadow beneath? Sorta like an rpg-character sprite?
Would make them stand out, enhance the feeling of perspective and you could animate them floating up and down to make them pop out even further.
edit: Played around a bit and just tried some random stuff. Maybe there's something that might inspire you.
Also, the gems don't really fit into the setting, what about spray cans or paint buckets?
Perhaps even different colored flowers/grass that sprout out through the ground?