For the majority of people, Social Security Disability benefits are not taxable. This is true for people who have income in addition to disability benefits as well as those who do not. (Most of the one-third of disability recipients who do pay taxes on benefits receive SSDI benefits, not SSI.
Mixing all three gives black. The CMYK color model (process color, four color) is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key (black).
SUBTRACTIVE colors are like paint. For additive colors, you can make yellow from adding red and green light. Or yellow, being a spectral color, means that light of a pure certain wavelength, around 570nm, is itself yellow. For subtractive colors, yellow indeed is a primary, and is the reason that the inks coming from most color printers are NOT red, green or blue, but rather cyan, magenta and yellow (and sometimes black).