If you don't get anywhere with Americolor, have a look at www.LorAnnOils.com they manufacture food colours and they have very carefully answered your question on their "Gourmet Foods" FAQ.
NO I'm not going to copy it here. You will need to download the positive statement of content from whatever manufacturer you choose for this client's information.
If you need another source there is Squires Kitchen brand in the UK also with a certificate of content. Use Google to find local distributors in your area.
And you need to get your client to write down for you the names of all soy derivative products and their levels that you must avoid. Because sometimes the word "soy" will not appear but the derivative will be present.