Base coat hair coloring

I was wondering if you could answer a question for me.  I have been having my hair color weaved for quite a long time.  The color is a very pretty golden blonde.  Although, my own color is a dishwater blonde, however they always complemented each other in between touch ups.  Lately, as I am starting to get older and my own color is looking a little more mousy and some gray coming thru, some people suggested I get my roots colored with a base coat.  I did do that a couple of times a few years ago but for some reason not sure why I didn’t like it.  Can you tell me what a base coat is and what it does because I was told it would not cover gray hair.  I was confused on how it would brighten up your own color but yet not cover the gray.  And also can you advise if this is the best way to go.  I have been hesitant because I really like my hair color but notice by week 3 or 4 it starts to look drab because of my own drab dishwater blonde hair underneath.

If you could give some suggestions and clarification on what a base coat is.

Thank you so much!