Let thy garments be always white; and let thy head lack no ointment. Let thy garments be always white - The Jews wore white garments on festal occasions, as emblems of joy and innocence. Be always pure, and always happy. The inhabitants of India are all dressed in clean white cotton, and to this is the allusion in the text.
The Targum says: "At all times let thy garments be washed and pure from the stain of sin. Acquire a good name, which is likened to the oil of anointing, that blessings may be called down up thy head, and goodness not forsake thee."