Air-dry earthenware clay (clay that hardens when exposed to air after sculpting) is generally designed for use in projects that don't require colour, or projects that are coloured with paint after hardening. However, for some projects, getting the right kind of colour detail is only possible with clay that is already coloured. To get these effects with air-dry clay, you can colour your own using makeshift powder pigments.
Soften and moisten the clay. Work it in your hands while mixing in water, a few drops at a time, until the clay is soft, pliable and slightly on the moist side compared to what you normally like to work with; this will help the colour powder stick and mix well.
Divide the clay into portions according to the colours you want. If the portions are small, cover them with cling film to keep them from drying out while you're working with other portions of clay.
Press your finger into each ball of clay to create a small cuplike indentation. Make it about a 1/2 inch deep.
Work drink mix powder into each ball of clay. Pour the powder into the indentation, then seal and work the clay around it. Continue kneading the clay until the colour mixes evenly throughout.
Repeat Steps 3 and 4 until the colour is as deep as you want it to be.
Wash your hands before working with the next ball of clay; this will keep the colour from the first section of clay from transferring to the next section.
Sculpt with the clay carefully to avoid getting dye on clothing. The colour may still transfer while the clay and dye are wet, but once it's dry, it will be fixed in place.
Apply waterproofing sealant to the dried, hardened clay.