Default Minecraft Textures.

Hello

I have been playing around with some textures in a mod that I downloaded and managed to make blue cows with black eyes and black pigs with white eyes (the pigs are creepy to come across at night.) That got me thinking, is there a way to edit the default textures that Minecraft comes with or is this not possible? I looked it up on youtube but all I got was a list of videos on how to make your own custom texture packs, which made me think that this may not be possible but then again, it must be, because the textures have to be stored somewhere within the files, right? I looked through many different folders and could not seem to locate the default texture pack anywhere, it's not even in the ResourcePacks folder, which leads me to believe that it may be stored in a hidden and locked folder somewhere, but maybe i'm just not looking hard enough.

If anybody happens to know where I can find the default minecraft folders, please do let me know, and help would be greatly appreciated.

Thanks in advance.