You have probably solved this already.. but for other people with the same problem:
The s-video signal is very sensitive to phase shifting, and cheap adapters and long cables may shift the phase just enough to mess the colors or even make it b&w.
HOWEVER, 50% of tv's dont support svideo trough scart correctly, and cause it turn b&w. This is very probably your case, like it was mine and many of my friends.. There are two solutions:
1) buy a svideo - composite(RCA) adapter, so the scart gets rca instead of svideo. This will result in bit worse picture quality than with svideo, but you got colors!
2) You have to modify your scart adapter by soldering pins 15 and 20 together, as such:
______________________
I I
I O O X O O O O O O O I
/ X O O O O O O O O O I
/_______________________I
This is very easy to do for anyone, i highly recommend it over the rca conversion because of the picture quality..
first open the adapter(usually there are no screws, so you have to brake the plastic cover.. use some plastic tape, glue or similar to put it back together), then locate the pins 15 and 20 which i have marked with X's..
solder them together with a piece of wire, and you got colors(if not, back to solution 1)!
Hope this helps!
edit: The formatting of my "picture" seems to mess up a bit, but you get the idea.. third pin in the upper row and first pin in the second row when you keep the adapter in similar way as the picture suggests.
edit 2:
Here's a better picture so you know which pin is which.. this is rgb scart so dont mind the names and the language, the important thing is to be able to locate pins 15 and 20.