Why am I getting cards of my opponent's colour?

[WiAiC]

I thought I'm only playing for my colour, but in some games, I keep getting cards of my opponent's colour, and led me to some mistakes. Sometimes, few mistakes in a row, 'cause I didn't aware the colour of the card.

I can't get any rules or tutorial video, hope someone can let me know how is this game actually played. I'm just doing clicking now.

[Tzinacantli]

You get your opponents' cards after you place 4 cards in a row (winning a round). The more rounds you win, the more cards of foreign colour you get

I make these mistakes too... blocking my own rows

[DoctorFianchetto]

When I encountered this I genuinely thought it was a bug where my own cards were transforming into my opponent's colour, perhaps due to me and that opponent trying to occupy the same spot at the same time.

I didn't realise it was part of the game. That seems like a silly rule. Do you have to get rid of your foreign colours by placing them on the board?