Choose one colour
On a suitable walk you were already planning, choose a colour and notice where it appears. Pointing to a sign, window or distant object is enough; you do not need to collect anything. Follow another colour if that interests your child. Consider traffic, weather and the setting before playing, and maintain adult supervision. The activity should fit the journey rather than distract from keeping it safe.
Make it a conversation rather than a race
You need not count who spots the most colours. Talk about a shade being light, dark or similar to another one. You can use the idea from a window at home as well. A day without an outing is not a missed assignment. Adapt how you take part to your circumstances, and leave space for your child to notice something entirely different.
Your next little step
Choose one idea that suits your family and try it at your own pace. Every family has different needs.
An example in practice
After noticing a blue door, you could imagine a story behind it instead of searching for another blue object. There is no need to extend the walk or complete a photographic checklist before going home.