For those of us old enough, remember when Labor Day signaled the storage of all things white, only to be dusted off the following Memorial Day weekend? Then there were "winter whites", a la anything creamy white.
Really, any color works for any season; it's the weight of the fabric that makes it seasonal.
With a little knowledge and maintenance, you can keep your whites free from yellowing, staining, and graying:
Strictly keep whites separate. If you wash your pure whites with a piece of clothing that is white with another color (i.e. a blue and white striped shirt) it will start to alter your pure whites.
Use less detergent. Detergent coats fabrics and acts as a magnet for stains.
Add about a tablespoon of dishwasher detergent with the laundry detergent.
No chlorine bleach. It will yellow or gray fabrics. (Ok for cotton, i.e. socks).
Lower heat in the dryer or air dry. Too high of heat will scorch fabrics, turning them yellow.
Wait until your deoderant is completely dry before dressing. The aluminum compounds in deoderants cause yellowing.
The best product: Oxi-Clean Stain Remover and Oxi-Clean granules.
To prevent armpit yellowing:
After wearing, turn your shirt inside out and spray with Oxi-Clean. Spray again before washing.
If it's already stained:
Add about 1/2 cup freshly squeezed lemon juice with oxi-clean granules in your wash.
Or, equal parts hydrogen peroxide and baking soda, followed by oxi-clean granules. If you have stains that have been in the dryer on high heat, they are probably there to stay.