Novice at work

So, I'm knitting the marble sweater and things are going well. I knit up the back in no time and have been working on the front. All is going well, until I got the the v-neck shaping. The pattern said Work to last 3 sts before marker,(center) k2tog, k1, join 2nd ball of yarn and work as follows...... Ok so I'm thinking what, join 2nd ball of yarn? Do I now knit with both yarns together....nah that can't be right?? Ok do I start a new skein of yarn now?? Well that makes no sense, who would join a new skein in the center of the sweater, on purpose.... Can't figure it out, see I'm still a beginner. Anyway, so what do I do, I start a new skein of yarn, the whole time thinking this can't be right. I knit and knit thinking how do you get a V neck out of this...Something is not right
Thankfully, while reading other blogs I found this entry and bingo it all makes sense. Duh....
After frogging back and working on it today, I'm almost back to where I was..

I should finish the front and I'll start on the sleeves tomorrow. I'm going to do both sleeves at once. I hope to be ready to seam it up next weekend. Wish me luck. Oh as you can see, I'm having the same mismatched skein issue on the front. I know I should stop frog and re knit, but I can't tell the color difference until after it's knit up. For now my plan is to knit it all up, decide if I can stand the difference or not. If not when I frog, I will be able to tell which skeins are the same and leave out the lighter ones. I think I'll end up with one extra skein.