The amount of air that escapes through the nose during their articulation is known as nasalization.  
R-colored ones result from retroflex or bunched contact and cause a lowered frequency in the third formant.  They can differ in roundedness, backness, and height, and Spanish ones are often described as tense, while English ones can be tense or lax.  Each has a unique sound known as its quality, and one that changes between two qualities during its duration is known as a diphthong.  The amount of air that escapes through the nose during their articulation is known as nasalization.  FTP, name these open-tract syllabic sounds in language whose English varieties include A, E, I, O, U, and sometimes Y.
R-colored ones result from retroflex or bunched contact and cause a lowered frequency in the third formant.  
vowels