Well, since it's edible, I am sure it's safe for soap. But how expensive is it? I say give it a try with a small purchase and see how it works for you.
One thing to keep in mind is that you probably won't really know how much of what micas or oxides you are actually putting into your soap, so recreating the exact same colors may be more of a challenge.
Also, if you are in any way concerned about vegetarian-type (not that you eat, it, just that sometimes a vegetarian or vegan doesn't want animal products in their soap), then Carmine is out, so you would need to avoid the pinks and reds because they might contain cochineal, which is made from bugs. (I am referencing the second link you gave, which states that they may contain Carmine.)