Cast on 3 ends with two different colors

How do I do this?
The pattern for making the right side of the body of a kitten states:
With US 2 needles and 2 ends of smoke colored yard and one of pearl colored yarn, cast on 4 stitches.

Sounds like you should be casting on with 3 strands of yarn held together. See if the pattern states this somewhere at the very beginning, maybe under yarn requirements.
Can you give us a pattern name or a pattern link?

There is a materials list, but it doesn’t give me any help.

That sounds like you’re to hold all three strands at the same time. Cast on and knit with them as if you were holding a single strand of yarn.
Any pattern name or link?

It is from the book Knit your own cat and the pattern is tabby kitten sitting.

How cute!

From the notes, it looks like you’re using multiple strands of yarn at once.

I don’t have a second ball of smoke, can I just estimate how much I think I’ll use and cut it off?

You can do that or you can pull from the other end of the ball, either on the outside or on the inside.

Like this?

Yes, the 3 strands held together as if they were one thick strand of yarn.