How do you change them? There seems to be no setting for chosing the colours you want to use globally. It's possible to change them for each beatmap but that seems like a lot of trouble for something that should be availabel in the skin editor.
Hi Shikamadoji! You can export the selected skin and import it to osu!stable client.
To change the hit objects colour, you can refer to its skin folder by going to "open current skin folder" in the osu!stable settings. Scroll down to find "skin.ini" file and you can freely change the colours in the "Combo:" command. (RGB colour code)