A Recolored sprite or texture is when the shape and form remains entirely the same with the exception of the item's palette.
The technique of recoloring has been used since the early days of gaming. It allows for developers to create additional enemies quickly and easily.
While the technique is often frowned upon within the spriting community when it comes to starting out with spriting, it has its place to be used, and learning how to quickly and easily recolor a sprite is an important skill to possess.
There are a number of different techniques to recoloring depending on how specific you wish to make your changes.
For a better understanding of the tools described in this entry, see the Paint article of the wiki.
Select the Pick Color tool and left click on the color you want to change and right click on the color you want to replace it with. Switch to the Eraser. Now simply swipe over the sprite while holding down the right mouse button. The first color will change to the second color.
A similar method can be used for entire sprite sheets. Select the Pick Color tool and right click on the color you wish to replace. Now, press CTRL + A, and then CTRL + X. This will cut the entire sprite sheet. Simply fill the solid color that is left on the document (which should be the color you wish to replace) with the color you wish to replace it with. Press CTRL + V to paste your sprite sheet back into the document, setting the secondary color to transparent. This will replace said secondary color with the color that you filled with.