Indeed.
I really wasn't under any illusions regarding the color, since I also have the Medicom Stormies which have a beautiful glossy finish to their white armour.
Anyway, the parts arrived yesterday and I quickly put them on one of my Sideshow Stormtroopers.
The color difference is quite shocking, and it does make Sideshow's look pretty ugly and cheap when inspected up close.
I think you'd have to repaint the whole thing to match the color, no gloss coat will help there.
As for the fit, I have my Sideshow stormies stock, no body swaps. The chest and abdominal armour, as well as the cod piece fit perfectly on the regular Sideshow body, but the thigh armour is way too large, so I kept the Sideshow one.
Here's a couple of quick iPhone pics I took this morning:
As you can see, the new armour really improves the look of the figure, but the difference in color and texture is inescapable.
Still, I'm happy for now. I'll give it some more thought on whether I want to get more loose parts.
At any rate, I can imagine how impressive the HT Stormtroopers must look, based on the quality of the loose parts I bought.