It would be great to have a tool, like the bucket, to change a whole color for another in a sprite, like clicking light blue with dark green would change all the light blue pixels in this frame for the new color, dark green.
In the current frame/layer, you can use uncheck the Continuous option in the Paint Bucket to affect the whole content of the current frame/layer:
If you want to re-color all layers/frames, you can use Edit > Replace Color (Shift+R key) and select the All option to replace the color in all frames: