This "fashion" of coloring the Euro coins emerged a few years ago as an initiative of some numismatic companies to reactivate the coin market during periods in which the official mint houses were not issuing new coins. For this reason, they began to color, mainly commemorative coins of 2 euros and some regular coins of 2 euros face value.
Although the majority of collectors did not like these manipulated coins, the truth is that many people ended up adding them to their collections. This action increased the demand for them and, at the same time, more companies were introducing a multitude of colored coins into the market, increasing supply.
The reality is that color alterations of the coins are “illegal” and although the main European mints were aware of the fact that companies were coloring coins for profit, they didn’t do anything about it. Well, initially there were some small initiatives of the mints to try and limit the production of these currencies, but they ended up not having any tangible effect.
Each year, there were more colored coins that appeared. You could find the same coin painted in a multitude of ways, and collecting all the variants was practically impossible.
Finally, many of the official mints changed their criteria and are now minting versions of the coins themselves, including several colors. That is the case with the Spanish 30 Euro coin which we referred to at the beginning of the post.