I went to the supermarket looking for lentils due to them being a source of protein and I saw a whole isle devoted to beans and lentils. The variation in color is astonishing (some were orange, others were spotted, some were red, etc.) Would there be any benefit of mixing all the different colors of lentils as opposed to consuming a single type/color?
Yes they differ. Red lentils get their color from a greater presence of carotenoids, which are a particular class of antioxidants. I’m sure green and orange lentils are higher/lower in still other compounds. I would not mix them before cooking, since red lentils cool faster than green ones. No harm in mixing them after they are cooked, though. Flavors are a bit different.
While this is not exactly what you asked for, here is an article explaining how to cook different types of beans and why some are hard and some others are softer. The article is published on serious eats from a biologist: https://www.seriouseats.com/baking-soda-brine-for-beans-5217841.
So, I would suggest against cooking all of them in the same pot as they probably need different cooking time, but consuming them all together is totally fine. I usually cook different types (black eyes beans and navy beans), add some vegetables and canned tuna and store in the fridge for my next day’s lunch (it kinda looks like a salad and it’s served cold).
More info on cooking different types of beans: https://www.seriouseats.com/beans-legumes-pulses-varieties-recipes-cooking-tips