Gold is KoGaMa's Currency, it can be used to buy stuff like skins, models and items.
Gold looks like a 3D "Sprite based" Cube, its color is gold, as its name says.
It will appear on the games with the [Gift] Icon as a button, when clicked that button, 3D Golden blocks will appear giving the player 100 XP (Gold reward from gift was removed on June)
Ways to obtain
All ways to get gold are listed on the Earn Gold page.
The gold block's counterpart are the silver blocks, They was really easy to obtain and (Probably) was the 0.001 of a golden block, and 1.000 of them was 1 Golden block.
Its appearance is the same as the golden block, but with black/white scaled colors.
The silver was removed because players made made to exploit getting silver. Some players therefore got unlimited silver. Therefore, Devs had to remove it.
There are still Silver blocks on user's profiles, but the Silver has been removed from the code.