How create var specified type on Go?

I have a function.

func doSome(v interface{}) {

}  

If im pass pointer of array struct in function, she must fill array.

type Color struct {
}
type Brush struct {
}

var c []Color
doSome(&c) // after с is array contains 3 elements type Color

var b []Brush
doSome(&b) // after b is array contains 3 elements type Brush

Maybe need use reflection, but how?