For the Asteroid color, yes they are generally similar to each other and it does shift (much like the background) In early production we did have asteroids coloured depending on their resource and we found not only did it look bad (think coloured polka dots) but because we have 20 resources it was difficult to tell some of them apart, along with that having to memorize a colour chart wasn't very fun. So we came up with the scanning system which promoted exploration, which I think works pretty well. Shifting back to a visual method of determining asteroid resource would undermine the scanning system.
I think you do make a solid argument for making blueprints invincible, or maybe just have pirates ignore them. I think that makes a lot of sense and would reduce player frustration.








