Hair Root Touch-Up: Preventing White Lines & Achieving Seamless Color

Question
I have recently begun dyeing hair to cover first greys which are around temple area, and a couple very close to my forehead, so they are noticeable and not easy to hide.  Now this is all new to me.  How is this workable with roots/  How do you do it so that you don't wake up the next morning, and discover, ay there's white showing??? Do you retouch roots before they show??? I notice those temple areas are the first to show.  But do you retouch all roots, when you see the first two or three showing or wait until there's more so you can more covered?? How do women keep those roots retouched without having to do this almost every day?? I just am envisioning myself retouching the first few, and the next day other's coming out since all hair grows at different rates?  Also I don't want to be the one who wakes up for a big day at work and has those temple hairs shining like a bright light! Please put this into real context for me.

Answer
most people touch up the root area every 4-6 weeks. try not to obsess about every hair as it grows in, rather use a temporary cover product. this is sold where you buy hair color, it looks like a mascara, and essentially is a mascara product that you can brush onto the little hairs that appear around the front, seemingly overnight.this product washes out and can be used as often as you need to between touch ups. you don't want to color with permanent color every time you see one or two grays.