Colourful digits useful in the nursery (5,7)
I believe the answer is:
green fingers
'useful in the nursery' is the definition.
I can't tell whether this definition defines the answer.
'colourful digits' is the wordplay.
'colourful' becomes 'green' (I can't justify this - if you can you should believe this answer much more).
'digits' becomes 'fingers' (finger is a kind of digit).
'green'+'fingers'='GREEN FINGERS'
Can you help me to learn more?
(Other definitions for green fingers that I've seen before include "Successful gardener's supposed attribute" , "Ability for horticulture" , "Gardening skill" , "Person adept at growing plants" , "Horticultural skill (or luck?)" .)