While I've used silver reflective umbrellas in the past, I much prefer using white ones (they do require a bit more power, though). I'm not a fan of the gold umbrellas. I like to gel my mainlight with 1/4 CTO lots of the time. However, a gold umbrella is substantially warmer than that. I like gelling flashes because you can have a full set of gels that arm you for just about any occasion, and you can fine tune the color with 1/2, 1/4, and 1/8 variations.

If you did go with a silver umbrella, gel you flashes with 1/4 each to counteract the coolness of the silver reflective surface.