I had similar experiences with Wellness dry ("Complete Health" - in the blue bag) with my two cats. Their poo was on the soft side and light colored (compared to other dry foods I had tried.) Also, it seemed more frequent. Before this, I had them on Wellness Kitten Health (green bag), then later tried other foods (Castor and Pollux Ultramix Kitten and Iams Healthy Naturals Chicken, amongst others) as they grew from being kittens to more adult.
After switching to Royal Canin (Indoor 27) it seemed to get better. (Firmer poo.) Currently they are on Merrick's Before Grain (Chicken) with a smaller amount of the RC Indoor mixed in. Poo is normal/firm and less quantity.
Anyway, from gleaning info here before, it seems like for certain cats, particular foods can be too "rich", causing stomach issues like this.
(Also, I always feed wet in conjunction with the dry, although I've not noted any particular stomach problems with any wet/canned food. I've fed them a wide range of wet food from Wellness, Petguard, Natural Balance, Avoderm, Fancy Feast, Eagle Pack, etc.)