I have heard this complaint about many brands, so I don't think it's a problem with the paint, but could just be something that happens when you have direct sun heating that air space between a storm door and a front door. Perhaps it is worse with dark colors.

It might be a latex paint.

Not sure if this helps but I used an oil based enamel on my front door that gets a lot of hot sun. The color is a sage green but I don't ever remember it giving off an odor.

I have a storm door too, facing SW, so I'm familiar with the potential heat between storm and door. I put in storm door with a screen that retracts, so I can leave a small opening at the top of the door for the hot air to escape.

I have the same issue. Its not the paint, it is the storm door glass magnifying the heat from the sun. You absolutely have to use a screen in your storm door. I have an Andersen with the disappearing screen. I only use full glass on very cold and overcast days. Even cold days when the sun is bright will give you a "hot pocket."