I'm not a vet or a doctor or even a real scientist. What I say comes from experience and what ice learned from reading, communicating with others including vets and zoo people, etc. somtwke it for what it's worth.
You can add sweet red peppers, squash, zucchini , kale, dandelion greens, etc to what you feed the crickets, superworms, locusts, etc.
Regarding supplements...for many years I have used a phos free calcium powder (Repcal) at all feedings but one a week (dusted lightly on the insects) and on that one day I alternate between a vitamin powder (Herptivite) with a beta carotene source of vitamin A and a phos free calcium/D3 powder (Repcal) (dusted lightly) for veiled chameleons. Using a vitamin powder with a beta carotene prOformed source of vitamin A means you may have/want to use a powder once in a while with a prEformed source of vitamin A ...just to ensure the chameleon gets some vitamin A without overdoing it. The same threory applies to the D3... We want to give some but leave the chameleon to produce the rest from its exposure to the UVB. We don't know the exact amount of anything that chameleons should absolutely have so we're trying to hedge our bets by giving trying to come close in as safe a way as possible.
The supplements done this way, along with feeding the chameleon an assortment of insects that have been fed well to make them as healthy as possible, appropriate temperatures, etc seem to keep the chameleon as healthy as possible. Doing it this way...my females almost always live to be 7 years old and the males longer.
BTW...there are many supplements out there and likely other ways of doing things that may be as successful. We're all still learning.
Hope this helps?
