If the color gets used again within the next row or so, you can leave it where it is and pick it up when needed. You may need to carry it to the end of the row if it's going to be used further along in the row or in the next row. If that's so, you'll have to catch the floats to prevent a long loose loop of yarn on the back of the project. If you're not going to need it again soon, then cut it leaving a tail to weave in. There are videos under Advanced Techniques to show you intarsia or fair isle knitting which may help.
Can you link to the chart or pattern?