d) For painting your texture, make sure that no texture is on your brush which prevents any selected color from being painted on the texture. You can achieve this by creating a new brush like this:
da) Click on the „Draw Brush Icon“ in the „Toolshelf“ (press „T“ if it’s not visible) on the left side of the „Texture Paint Editor“
db) Click on the number at the right of the „Brush Name“ in the „Brushes Panel“ of the „Properties Panel“ of the „Texture Paint Editor“ in order to make that brush a „Single-User Copy“:
dc) Now check in the „Texture Panel“ of the „Properties Panel“ whether there’s a texture:
If you see a „Checkerboard Image“,  …
… then you can start painting with the color selected in the „Color Wheel“ of the „ColorPicker Panel“ in the „Properties Panel“
....