PNG got green background when imported?

I imported a png with a transparent background into unity, and randomly there's green where its transparent. I'm making a 2D game with pixel/retro graphics and the green background png appears much clearer in game compared to other pngs which are just black where its transparent. I have no clue what I did or what this is called, but I want to recreate this effect in my other pngs but I cannot find a setting anywhere to change this. The background is only green when imported to unity, outside of unity the background is just clear. Here's a picture of the green background:

How would I make it green on all my other pngs? Thanks!