"Rainbows" are often due to swelling of the cornea (corneal edema). That does not happen in most types of glaucoma including the most common type "Primary Open Angle Glaucoma) POAG It occurs in acute angle closure glaucoma which is rare except in Asians. It is usually accompanied by very blurred vision, red painful eye, fixed pupil, headache, nausea and vomiting. If your ophthalmologist thought you had ACG he/she would recommend hole in iris (laser iridotomy). There are many other causes of rainbows besides corneal edema, i.e. cataracts, other types of corneal disease, etc.