Choosing colours "without baggage" for item comparison

I am sketching an interface that allows people to compare multiple items side by side.

The interface implements the following requirements:

• users can add new items to the comparison
• the differences between them will be highlighted
• there should be a visualization that maps the ingredients of an item to a consumer

The comparison algorithm can handle N items, so if one has a wide screen - they're welcome to add as many items as they please. Realistically, I expect that people will usually compare up to 3 or 4 items.

To link the items on the left, with their ingredient-consumper maps on the right, I use colour, which brings me to my questions about choosing a colour-scheme:

1. what scheme is best suited for conveying qualitative data?

The items are not ranked from "good" to "bad" or "healthy" to "unhealthy", they're just different items.

2. what scheme is not "preloaded" with meaning?

For example, in this illustration Ipsum is green, which is associated with "good", "safe" or otherwise positive in most cultures. This might lead users towards wrong interpretations.

3. how to best deal with the addition of new items, colour-wise?

If I use a triadic scheme for maximum distance between 3 colours, I'd have to switch to a tetradic scheme when a 4th item is added - which would change all the previous colours. I thought of choosing a qualitative colour-scheme from Colorbrewer for 7 items, and using those colours only. This avoids the reshuffling of colours, but inevitably, some of them will be green/positive, others will be red/negative.

My feeling is that there are conflicting requirements, and perhaps I am asking the wrong question - maybe using colours here is already a mistake, and maybe the diagram on the right is also not the most suitable one. Thus, besides asking for answers to my three questions, I also ask for advice on how to tackle this, thank you!