How do you cast on beginning of row and new yarn colour?

[caraorr1]

Hi,

I am new to knitting. How do you cast on at a beginning of a row also keeping the stripe colours correct? i.e. I have just finished the previous stripe in main and need to change to contrast yarn.

If I cast on new stitches at the beginning of this next row in contrast won't that mean the main and contrast are together in one row?

The pattern says:

Keeping stripes correct, shape sleeves.
Cast on 47 sts. at beg. of next 2 rows.

Can anyone help?
(Each stripe is actually 4 rows altogether)

Thanks

[suzeeq]

Use a knit CO and you'd probably do it in the contrast color because you work across the cast on sts, so you'd want it all in the new color. The CO doesn't really make its own row, it would just be part of the row that's knit into them.