I found a huge cashmere sweater at a thrift shop this morning(2 and a half bucks!)

and I want to recycle the yarn. The problem is: it's the color of oatmeal; not a good color for me. So I want to dye it. I've never dyed yarn before, so any advice would be appreciated. One question I have is: should I frog first and dye second, or can I dye the entire sweater and then take it apart? Would that make the color more variegated? What should I use to dye it?
Unrelated to dyeing: is cashmere a good yarn for spring/summer, or should I save it for a winter project? Thanks in advance!