Need advice on shade selection/loreal Color spa

Hi
I am trying to switch from using permanent haircolor( Clairol Nice and Easy) to semi-permanent color but I need help with shade selection. I have very short hair ( Winina Ryder short), hazel eyes and somewhat medium complexion that burns then tans). I had been using one part Naturally tawny auburn with one part light brown on my hair but the problem was that the top of my hair would get lightened by the sun and end up looking brassy while the sides and back would remain darker. My sister called it the "mod look" not what I was going for. I had heard good things about Color Spa but need help with a shade. My natural color is a medium brown but I would still like some red in my hair. What about their Chestnut shade? Going totally red is too much upkeep and I want something natural looking and since I know have a tan, red seems out. Any suggestions?
Sorry this is so long but I knew this would be the place to turn for help.

Thanks
Susannah