What Muppity said, except it's the girls that last longer

The Shetteles method is Based on a 28 day cycle & ovulation on CD14;
If you want to TTC pink you probably stop BDing on CD12.
If you want to TTC blue BD on CD14 & CD15.
The egg only lasts for 24 hours though - best used with OPK's too.

If you don't care what sex (or you dont have a regular cycle) just BD every 48 hours the whole cycle!

There are a few things you can do to gender sway if you're after one or the other. There is a chatter thread for it too