Melisa,
I am sure it is one of the crab spiders, in particular one of the flower crab spiders, and quite possibly Thomisus onustus; a female. Here is a nice page of unidentified Thomisus species, showing some of the colour variation, and describing how they can change their colour to match their flower
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http://www.biodiversityexplorer.org/arachnids/spiders/thomisidae/thomisus.htmMore and very good detail on the Thomisus genus here
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http://www.jorgenlissner.dk/Thomisidae.aspxAnd that gives a clue to IDing T. onustus:
"The species is easily identified by the triangular abdomen and the protuberances that carry the lateral eyes."
Also, the lines across the width of the abdomen distinguish it from Misumena vatia (which can also change colour), which has lines that run lengthwise along the abdomen.
I get T. onustus in my garden, in various colours and patterns, including a marked-whitish one like yours.
They are not worried about having a go at prey much bigger than themselves, such as butterflies.
As with many a titchy creature, the closer you look, the more fascinating stuff you see.
If you look closely at one of the (colourful) females, you might see a much smaller brown male on her. There's an example of that in the top-left photo in the first link above.
Mike