Graphtint pencils by Derwent. I got the initial box of 6 "tints". They are a water soluble graphite with just a hint of color. I think I am going to enjoy using them. They do also come in 24 shades but I am thinking that I'll play with these 6 for awhile first.
They are different from "watercolor pencils" which do not contain graphite. I used 3 tints in this sketch...a dark indigo shade, a Mountain gray shade and then just a touch of Ivy green around the label. It's quite lovely for studies like this. I hope to put them into my sketching bag and try them more. So easy to use with just a water brush to activate. Here's a look at the tints: