HAIR COLOUR: Advise Needed

Occasionally when I am getting bored with "my look" I start to think about colouring my hair. I have even gone so far as to purchase permanent colour from the store - but have always chickened out and taken it back. I have A LOT of hair so doing permanent colour is a big commitment. I also worry about damaging my hair,making it more frizzy or having to colour the roots continuously while it grows out.

My personal solution to this dilemma is to take the semi-permanent route of Clairol Natural Instincts. I have used this colour several times over the past 5 or so years. I even used it before my wedding. I have tried various shades. Sometimes I am happy with the results and sometimes not. The thing about this hair colour system is that it has no ammonia and low peroxide - so ultimately it is supposed to be fairly gently on your hair. You can not really lighten your hair with it, but you can enhance your natural colour, go darker, or add certain hues, such as red.
I usually prefer an even colour and thus, my options are fairly limited because my hair is dark to begin with. I can not decide if my hair is medium or dark brown. I guess I try to call it medium because I have more colour options with medium. Clairol has a pretty good website that you can go to for shades and colour suggestions. I have also called the hotline many times:
1-800-252-4765

This is my hair "before". Is it medium or dark brown???

Today I am deciding on whether to go with:

#20 Hazelnut - neutral and should enhance medium brown hair
#18 Pecan - golden and should add golden tones to medium brown hair
#28 Nutmeg - neutral and should enhance dark brown hair

Any advise????