The Tibetan word for the hues of a rainbow is འཇའ་ - a nicely balanced looking word, which is here playfully created in rainbow colours in the style of traditional Thangka painting.
The calligraphy below translates as:
"Visualisation meditation - Clearly Visible but insubstantial like a rainbow shining in the sky"
དམིགས་སྒོམ། སྣང་ལ་རང་བཞིན་མེད་པ་ནམ་མཁར་འཇའ་ཚོན་ཤར་བ་ལྟ་བུ།
This refers to the various stages of visualisation which are practiced as vividly translucent, not solid - just like the luminous colours of a rainbow, which are impossible to physically catch hold of.
Acrylic paint on Ivory mount-board, 21 x 19 cm