One common form of customisation is a fabric change. I get requests like this quite often and the good thing about them is that they are easily accepted.
Sometimes I get a question whether some particular colour is available in some fabric. One way to find out is to have a look at the AJ Group catalog. Sometimes this is a little tedious job to do so I finally managed to ask the factory for a list of available colour-material-pairs.
The list is now moved to the info-submenu as its own item. Here is a link.