[Lazy_Perfectionist]

Yep. As well, here's the quick answer to a color exchange- there may be a more elegant way.

Under the image's main menu-
Select->None.
Under the toolbox-
Select Regions by Color (Shift-O)
Uncheck all boxs (Antialiasing, Feather Edgess, Select transparent, sample merged).
Set Threshold to zero (essential)
Click on a dot. Voila, you now have all instances of that precise color selected.

Select the Bucket Fill (Shift-B)
Defaults: Opacity (100), Mode Normal
Important: Select as the affected area "Fill whole selection" this way, you will replace all the dots at once.
Select BG color fill

Select yourself a color- I suggest setting the palette back to default with the mini palette right next to the big palette. The background white is 255 255 255.

Now click in one of those tiny little dots in your previous selection. Done.

/Lecture mode: off. Thinking: resumed.