Adam nailed the palette, which is cool, saves me some explaining, thanks man
the other things i mentioned are basically that you should correct the perspective and unify the shading. Your building in front is shaded nothing like the buildings behind it, they should share a light source (this will help also in letting you share colors in many cases). You need to pick a method of describing the forms and stick to it, and also make it believable. for instance, that building that is quite dark between the two blue/gray buildings, there is absolutely no reason for it to be in shadow. none at all. if it isnt in shadow, and is actually just a dark building, i think you need some better way of describing this, at least by lightening the front plane like the 3 buildings around it. As far as correcting the perspective, the bulding in front is shown at a completely different angle when compared to the rest of the buildings, which are in a bizarre orthogonal distorted view as it is. Drop down a vanishing point or two would be best i think, since you have enough shades to AA the lines, but you could also just do the entire thing where lines on the z axis are displayed as (-45 o) the way you have in the back. regardless, the front building needs to be completely redrawn so that it fits, otherwise you break the percieved geometries and this is very bad unless you are doing in on purpose.
hope that helps explain things
