Be sure to clean the grout beforehand, as this pen will cover dirt, so if the surface is clean, it will cover easily.
There are 11 grout colors: white, winter grey, light grey, grey, dark grey, black, ivory, cream, beige, brown and terracotta. You can see all the colors here.
Promising review: “I have 12” white tiles throughout my house and they are 20 years old. I kept them looking nice, but the grout was still darkened. I cleaned the grout and let it dry well until the next day. Then I used the grout pen and it looked like new. When the tip of the pen starts to wear out, I just pull it out and flip it over, and I can use the same tip for the whole house. It takes a while to do, but it looks so good that I only do it sections at a time until I'm finished. I applied the grout pen and wiped the tile borders with paper towels, so no other cleaning was needed. ” —Amazon customer.
Get it from Amazon for $8.99+ (available in narrow or wide tips).