I'm concerned that the clear ones would create too much extra labor for the tile guy - everything has to be so perfect underneath!

Painting the tile pattern on the reverse of the clear plate? Would protect your artwork and disguise the switch as much as you like. Might want a small rectangle of either the white or blue just so you can find the switch!

Or, along the same lines as Kathy said, you could probably print off a copy of the tile (equal ratio, of course) and cut out the section you need to "back" the switch plate cover.

Or simply do what most people do and use white or off white switches and covers.