Color blocking is a bold and overstated design. Whether I like it or not depends on specific style and colors. For example, in the picture, I do like No. 2, and 7 and 13 are ok, but I really don't like No. 1, 8 and 12. And I don't think it is much helpful for slimless. By contrast, wide and lateral blocks help reveal the physical bigness.
I like #4 a lot, but you'd have to be tall and skinny to pull it off. In general I'm in favor of color blocking--I hope it stays partially in fashion at all times because it affords designers and wearers many options and is striking if done well.
I love color blocking simply because I love a bunch of different colors in my clothes! I think the trick to color blocking is choosing shades of the same color family like in different hues (royal blue and sky blue) or choose complementary colors (black and white). I am not sure if color blocking in general is slimming though, but if the dress is something like the this
Color blocking is the "in" thing and yes it works well. The trick is getting the right or appropriate color combinations to work for you. Mixing black with certain colors can enhance your look or appearance. On slim people, it rocks!
On people with some extra weight, it can help to conceal those parts not wanting too much attention by taking the eye elsewhere...
You are SO right, Cheeky Girl! Colorblocking chosen to enhance a person's figure or detract from a flaw takes advantage of optical illusion in a brilliant way. But, being bold, be careful that you choose the right pattern and colors for your body type and personality. Example: vertical angles in the middle will hide extra pounds, horizontal stripes will shorten and fatten, vertical stripes (especially lightly hourglass-shaped) will slenderize and heighten a person. See: both lines are the same length <-----> >-----< but optical illusion, as is done in color blocking, tricks the perception. #12 and #13 in the picture at the top will slenderize any tummy, but it can't work magic. To answer your original question, GmaGoldie, color blocking on fitness clothing gets 2 thumbs up from me! (short, tiny bit of a tummy)