I only recall the sith synthetic crystals having a chance to assplode. The jedi used natural crystals. I suppose an explosion could have been possible there too, but they weren't being as harsh as the sith who forced the crystal to bend to their will. I do believe the color was revealed upon activation, but the change happened during the process when you were meditating and connecting with your lightsaber. I think there was even once when a saber changed colors after it had been made and used for years. Cannot recall if that was NewCanon EU, legends, or one of the tv shows.