everything is yellow

When PJ was about 20 months old, his group at daycare started working on colors. The first color they introduced when he was there was the color yellow. As my son is not shy and loves attention, he learned that the correct answer to "What color is this?" was yellow. Even when they moved on to the next color, he still thought the color of everything was yellow. It took a while before we had other colors in the rainbow.
It was a temporary phase. For the past few months his favorite color has been declared to be red.