Yeah, you have flash, shade and full sun mixed in different shots. That makes it near impossible to get right. In each case, the top image looks somewhat over saturated, with a slightly green bias. And the bottom version looks more faithful, but a bit cool with some slight magenta/blue cast. It's impossible for us to know which is correct, which is more accurate and which is not, since we can't see the original items. I am viewing the images on a graphics quality computer monitor that's regularly calibrated, but am using Windows Explorer browser, which is not calibrated. So that's another big variable effecting color.
It's a problem working with mixed light sources. For best accuracy, you must select one particular type of light and avoid mixing. Most fashion and product photography is done in studio where a set of carefully calibrated and powerful lights are used as the sole light source. Reflecting off of an unknown item like a piece of styrofoam adds another variable... who knows if it's reflecting accurate light or if it's also adding some tint to the mix. Shot in a studio, you can get different looks by bouncing light using reflectors that are white, silver, gold or various mixes. You also might use a flag to hold back light, or a grid or snoot to direct it more precisely and prevent scatter that the camera might pick up.
So try just picking one light source... Just not direct sun because of the heavy shadows it creates and because it's too variable... changes color throughout the day, not to mention clouds that come and go and the constantly changing position of the sun. Other than that, shooting digitally and thanks to Custom White Balance it doesn't matter very much what light source you use, so long as it's uniform.
Shooting RAW will allow you to better adjust colors later, if needed. Shooting in-camera JPEGs will apply various pre-determined settings, including color temp and tint, to all your images. J{EGs are much harder to adjust later on.
Next, as others have mentioned and I've already hinted, you must set a Custom White Balance in the light you have chosen to use. Use a proper gray card and incorporate it in some test shots during the shoot, keeping those shots for reference on your computer. There are also MacBeth Color Checkers, as someone else already mentioned, that have a series of squares showing a full range of colors. If you also incorporate one of those in your test shots, you can see during post-processing if there is a particular bias toward or against certain colors, and adjust accordingly.
Finally, after the shoot you have to process the images using a calibrated, graphics quality computer monitor. None is perfect or can display the full gamut of colors captured. A print made from the image is likely to show wider color spectrum. A web-sized image is likely to show less. If making the images for online display, don't worry too much anyway. Some browsers do not adhere to any particular color profile and most people use consumer grade, uncalibrated monitors to view online. Most online retailers selling products that are colorful put a disclosure on their website, that basically says "colors shown are only an approximation because the computer you're using to view images on this website is a cheap POS that's incapable of rendering color accurately and isn't helped in the slightest by sofwares that don't adhere to any standard either". Okay, they say it nicer than that, but you get the idea.
It is true, too, what Jurgen wrote. Some fabrics and colors simply don't render well in various media.
All you can do is do the best you can. And that means controlling the source lighting as rigidly as possible and being careful to set an accurate, Custom White balance, and then processing the image through an equally carefully controlled computer system, to make an end product image (for whatever purpose you need) that's as close as possible to reality.
In print or online, it ain't never gonna be perfect, though, so you might want to include a disclosure. Most people who buy online are delighted and amazed how much better things actually look when they receive them.
Now you know why fashion photographers get paid the big bucks! It can take a lot of expensive equipment, extensive knowledge how to use it, and many hours or even days to set up the lighting (especially outdoors) for a session that only takes minutes to actually shoot.
Oh, and maybe it's just me, but I'd think dresses and any other sort of clothes would show off a lot better on a model, rather than on a mannekin. 
