Pallete
Left click on a store color to set it to the primary active color.
Double click on a store color to define your own color.
Tab switches between active colors.
Left click can also be used to switch between active colors.
Paint
To paint voxels, first enable the paint tool.
While the paint tool is enabled, pressing the left mouse button on a voxel sets the color to the primary active color.
Dragging the mouse after clicking on a voxel will paint other voxels.
Bucket
To paint multiple voxels at once, first enable the bucket tool.
While the bucket tool is enabled, pressing the left mouse button on a voxel sets the color of that voxel and all touching voxels to the primary active color.
Dropper
To pick up colors from voxel, first enable the dropper tool.
Click left mouse button on a voxel to set the active color.
Hold ctrl and click left mouse button on a voxel to set the last clicked stored color.