reduce function gives me undifined after second iteration

I’m a bit new to javascript world and I’m really confused by this piece of simple code and don’t know what is the exact problem.
I want to pull out all the colors and add them to a new array.
here is my code:

const data = [
  {a: 'happy', b: 'robin', c: ['blue','green']}, 
  {a: 'tired', b: 'panther', c: ['green','black','orange','blue']}, 
  {a: 'sad', b: 'goldfish', c: ['green','red']}
];


const colors = data.reduce((total,item)=>{
  let tempArr = item.c
  total.push(...tempArr)
},[]) 

console.log(colors)

>Solution :

A function that doesn’t contain a return will return undefined. Your reduce callback doesn’t contain a return. Fix with

return total;