 The preferred technique is sunk relief, where an area around each letter is carved out, leaving the letters at the original surface level, now higher than the background.The stones are often painted in symbolic colours for each syllable ("om" white, "ma" green, "ni" yellow, "pad" light blue, "me" red, "hum" dark blue), which may be renewed when they are lost by weathering.Along the paths of regions under the influence of Tibetan Buddhism, mani stones are often placed in long stacks along trails, forming mani walls.