I use 2 colors of the same brand when coloring my hair because lt brown is a bit too dark and dark blonde isn't quite brown enough. My question is...actually I like to use a bit more than 1/2 tube of lt brown and less then 1/2 tube dk blonde. Any tips of how measure when I can't see through the tube, lol and its hard to just guess. Thought others might have had the same problem and wondering what you did? Any tips appreciated.

3b, fine textured,thin and normal to high porosity.