Board Game Arena

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.

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

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?