Slip stitching

Please can someone advise ?
I have reached the collar part of my pattern and it reads as follows
Slip first 15 stitches onto righ hand needle, join colour A ( this is the easy bit so far) then knit to last 15 sts,sl1, turn

So what am Ito do with colour A also?

Confused right now
Xx

After you slip the first 15sts to the RH needle, knit across to the last 15sts using color A. To use or join this new color, simply start knitting with it leaving about a 6 inch tail to weave in later. The first stitch or two may be a little loose but you can always snug it up later.
When you’ve knit until there are 15sts remaining on the LH needle, slip one, stop and turn to the back. You’ll turn as if you were at the end of a row by switching the needles in your hands.

Can you give us a pattern name or a link to the pattern?