Hello again Suzuk,
Glad you like the look of the Cocobolo. The color can vary (sometimes the rusty orange is more predominant than the off-black), but the sound is pretty well defined. Cocobolo is a true rosewood (dalbergia retusa), and it is often said, that along with Honduran rosewood, it is the only true substitute for the rosewood sound you used to get with Brazilian. Some people hold that it is actually superior - it is a bit denser. As such, you would use it as you would a top quality rosewood - for backs & sides.
The topwood is indeed spruce: German Silver. Since it is just rough sanded - no finish - and with my poor photography, the photo doesn't show how pretty it will look later. Spruce / Rosewood is a classic combination for concert guitars, but people seem to like it in ukuleles too.