I don't believe they are always white, I see this type of spider in many different colors, Saw one a few days ago that was as yellow as an opuntia bloom, got side tracked and forgot to get a pic of it. I cut the branch this one is on and put it in a critter container, in the process of of the move he dropped the bee and left the bloom, it started to change color to green, took this pic about 2 hours after my disturbing him, you can see the green starting to show in a couple areas.