When you have fair size pieces of cardstock left over from making a card, keep them for making another card or project but to prevent a chaotic scrap pile I suggest that you "file" them in colours. You can use hanging files, boxes or any other storage medium that suits you. I use plastic suitcases that the children used to store their lego etc in and I have them labelled with the colour on the outside. When I need a specific colour I grab that case and take it to my desk to select the appropriate piece.
Have a wonderful weekend!