Very nice work. You need to make that into a tutorial!
On the yellow building, two things: 1) The building does not look like it is the same color all over. 2) I would use some kind of "digital eye dropper" program to get an idea of the variations of colors on the building. With the program I've got, DigitalColor Meter, on the Mac, with the lighting in your photo, on my computer I get;
Yellow bldg. R149, G124, B81 - You are almost dead nuts on that at R148, G125, B90 on your model. There was also some R159, G131, B90.
The yellow bldg. ledges look rusty. R133, G100, B93 Right now yours look a little light.
On the green bldg. I get R158, G171, B162.
The green bldg. ledges look darker, maybe rusty too. R147, G137, B140.
The lower ledge is darker still at R136, G133, B124.
Merry Christmas. Please take this as, "WOW, beautiful work, I would love to help you out!"...

...
Robert