Help me in reading this pattern...I'm a dope

Hi Everyone!
Ok…I’ve got this pattern to do a pair of socks on one circular needle. But, and you all know with me there is always a but :wink: , if i want to use only one color, instead of the two that the pattern calls for, do I cast on the 24 stitches or do I cast on more. I’m not sure when a pattern calls for using different color yarns, when you knit do you knit the yarn as one color? I hope that makes sense. Anyway the pattern is a free pattern and here is the link. Thank you all, I know someone can tell me!
:thumbsup:
Beth​:heart::heart::heart:
http://www.straw.com/cpy/patterns/cotton_chen_whisper_slipprs.html :shock: :shock:

When you use two yarns together, they are knit as one yarn. If you use only one yarn, the whole thing will turn out smaller, because the yarn won’t be as thick. If you have a yarn that is about 3 st per inch, you would follow the directions as written.

Thank you, I think what I will do is co and measure the gauge to see how that works.
Thanks again!
Beth♥