Is it a good idea to change your hair color from blonde to black?

I would suggest not. Most likely, you will not be able to get the blonde back to its original color without letting it grow, then cutting it to where the roots have grown out. So you say your original hair color is blonde. Okay, that's not a bad idea, sort of. But, I would say not to do this, because your eyebrows are going stay blonde, and it just looks weird. So don't do it, okay?