If ever a color were to be associated with an emotion (OK, blue, we see you), it’s got to be yellow. Upbeat and welcoming, it’s a hue that’s easy to love. But it can be tricky to use when decorating.

M&S has launched a competition for young people to create a winning design for this year’s M&S and Young Minds Hello Yellow kidswear collection. Working with the mental health charity, the retailer is ...