viewtopic.php?f=26&t=74911&start=20#p1172243
I use this method now too and it can give some very nice effects quickly.
So, in short, start out by drawing the structure and giving it the desired shadings, then apply the noise-method, tweak the colors to a desired outcome (as the original colors may have become a bit darker after applying the noise-method).
There is another thing I would like to comment on, but that may be my personal taste... So feel free to ignore this comment

The shadows under the roofs...
Be careful with that... Most things in OpenTTD dont create shadows... And if they do, they dont create shadows like these (as now it looks like the sun is straight above the roofs and even though there is not a real agreement over where the sun is, it is not straight above structures
