I try to follow this:
Paint window black
Paint window with VMC 49 Oxford Blue, try to leave the slimmest of black line as a frame of sorts
Paint an L with the point of the L in the left hand corner, always, using VMC 60 Intermediate Blue
Fill in the L, and don't be neat, with the Intermediate Blue
Take a off white and paint another L over the previous one.
Then add 2 dots in the right top corner. 1 big, 1 small.
I cant take credit for it, and to be honest, I dont even know where it came from. I still struggle with windows too, but in my opinion, this makes a nice colored window.
Here are a couple pictures of a hummer I did with this technique
Good luck!