"This may be a goldenrod flower crab spider, judging from the outsize front legs. Flower crab spiders are crab spiders of the genus Misumena with holarctic distribution. The goldenrod crab spider is the largest and most well-known of the North American flower spiders, commonly seen hunting in goldenrod sprays in autumn. It can change its color between white and yellow to match the flower it is sitting on. The color change takes a few days."

Thanks to Jennie for the identification.
Mr PGC