Yes, the color of an insert is simply a way to tell how firm one is, &/or how thick it is. The manufacturer color-codes them so we can identify them easily & make sure we're using the ones we want. HPI's inserts are probably the best example of this, as they have a number of different ones, & of course each has its own color to identify it with. And in case you were wondring, we have different kinds of inserts because they can have a significant impact on how well the tire works. It's a bit like how full scale race teams make adjustments by changing the air pressure in a tire(more pressure would be like us using a firmer insert).....