Hi shunyata and welcome!
I'm surprised at some of your results. Zucchini and broccoli were staples for me in the first few months because I found them so reliable. I ate them almost every day and never had issues. Other veg on my safe list: spinach, asparagus, okra, globe artichoke, rutabaga/swede, onion. Carrots were another story - though ostensibly low in starch, they always turned fully purple, and when I ate them I reacted I woke a bit stiff the next day.
Starch actually leaches out into the water when you soak or boil veg. Think of a pot of water after cooking potatoes or pasta -it's cloudy and thick from the starch. In the early days, in an effort to make carrots less starchy, I tried slicing them into medallions (to expose more surface area for starch to leach out), soaking them, rinsing, and then boiling them. I didn't react afterwards, but I didn't do it very often because. If making a stew I would just soak overnight. (By this time my symptoms were under good control so I can't say whether it made a difference or not.)
I only ever tested raw veg, not boiled. Doing that I noticed some veg just had streaks while others went full purple. Veg with streaks were generally ok, full purple or black were not. Maybe try testing when raw, or else rinse off your boiled veg before testing in case some of the leached out starch is clinging to the surface?
A neat trick I learned from a poster here is to put ginger and water in a blender, strain, and then let the liquid settle overnight. The starch will settle to the bottom and you can pour off the ginger extract. I haven't tried it with any other foods, but I wonder if it could also work with starchy spices like black pepper...
Suspected USpA. HLA B27, xray, u/sound, blood tests all -ve. Ancient history of plantar fasciitis, SI joint pain, knee arthritis. Recent history of tendinitis, neck pain, debilitating finger pain and stiffness (especially mornings). No diagnosis, no meds.
2010 - stopped eating dairy
2012 - stopped eating wheat
2014 - stopped eating all grains
Jan 2017 - discovered NSD - 98% improvement in symptoms, continually amazed by my results, wish I'd found kickAS sooner