Since your looking for a used bike, really any color would suit your needs. As with any purchase of a used machine, condition, condition, condition... What was the owners schedule of maintenaince. How often did he change / clean the air filter, change the tranny fluid. Did they every repack the swingarm and wheel bearings. What has he done to the engine, replace the top end, or bottom end bearings... There are the questions you want to get answered
Any of the different brands of bike will be fine, search around for the best condition for the money. Sometimes it takes a little while to find the "right" bike, but its out there waiting for you.
Good luck.