based on the work ive done at a plastic mold injection company, its as simple as pie to change the color of the plastic, why is it so difficult for them to sell us more then one color case?
It's simple, but still a time investment in the colour change process. They'd easily be able to make short run quantities of other colours, but with make-ready costs added in they'd have to charge significantly more on a per-unit basis to recoup the additional costs.
To be fair, I do plastics extrusion work. I'm aware of how injection molding works, but I haven't done it personally.
For us, changing the colour of our product incurs approximately a 1.5hr delay as the old coloured plastic is fully purged from the die and the new colour takes it's place. It's trivially easy to do - flick a switch, swap the coloured plastic in the hoppers, switch the flip back, but it's still 1.5 hours.
So, that's 1.5 hours of production time my company needs to pay for - that price is added in to the product cost.
When you order a product, you're already paying for a chunk of set up time which is factored into the cost. The actual production cost of the product outside of the set up time is ridiculously small, and the set up time is a fixed cost irregardless of quantity. Thus why you get bulk discounts - the costs which scale upwards with production are comparatively small.