Carmel used to color some vitamin D gel caps may cause problems in some people

Skin hives and eczema patches along with itching.
Common cold like symptoms with sneezing, runny nose and rheumy eyes.
Breathing trouble which can turn into asthma with noticeable wheezing.
Inflammation and puffiness of the facial tissue.
Insomnia and severe headaches that can result in migraines.
Digestive problems with nausea, vomiting and diarrhea.
Severe life threatening symptoms are known as anaphylaxis and can cause the blood pressure to drop suddenly with the patient losing consciousness.

Caramel color is one of the most widely used colorants in foods - soft drinks as an example

It seems doubtful that you are allergic to carmel in some vitamin D supplements if you are not also allergic to soft drinks

Costco and Nature Made are examples suppliers using Carmel

Bio-Tech is one of the very few suppliers which uses NO additives

See also VitaminDWiki