What's the budget?
Crayola is the cheapest color pencil. Not a bad brand.
I recommend a set of sketch pencils that range from 6B to 4H to help with light to dark values.
If you want to splurge on better color pencils prisma scholar color pencils are a good choice.
Honestly the list can go on and on. You didn't specify what kind of art he's into. Watercolor? Acrylic Paint ? Color pencils? Markers ? pastels? Pens?